More than one audio codec on a PC mobo

[Joerg]

miso wrote:

Joerg wrote:

krw@attt.bizz wrote:
On Tue, 25 Feb 2014 14:01:26 -0800, Joerg <invalid@invalid.invalid
wrote:

Folks,

The AC97 standard describes only up to four sound chips operated
simultaneously, on page 21:

ftp://download.intel.com/support/motherboards/desktop/sb/ac97_r23.pdf

What if one would like to connect, say, 20 of them and all are supposed
to run nicely synchronous? Like in a digital mixer board for music.
Why AC97? There are dozens of DACs and CODECs around with all sorts
of interface options.

The goal was to use sound chips because of their attractive pricing
while offering 20+ bits of dynamic range and potentially high sample
rates. Is there another standard that comes to mind?

I know how to roll this using individual ADCs and DACs but that gets
expensive. Plus we'll have to write our own drivers and all this fun
stuff.


If you don't want to roll your own cards, find a Magma PCI cage. I can drive
7 sound cards at once on mine, well on Linux. No idea about windows. My
Magma was from an old recording studio. I wouldn't want to pay the price of
one new, so look on ebay. And ignore all the buy it now assholes. I got mine
for about $200 plus change years ago when they were worth something.
Nowadays they have fancy multichannel soundcards. You need the cage,
backplane, and most important, the freaking PCI host cards. One your your
PC, the other in the cage. So an eight slot Magma runs 7 PCI cards.

If you were really clever, you could build this yourself. They use Pericom
chips and off the shelf PCI backplanes. I found it easier just to by a Magma
and cheap sound cards rather than make a project out of it. The setup is for
SIGINT, so the cards works independent of each other. But there is an
opensource Linux program for multi-channel recording.

TI makes some chips that are 8 channel oversampled converters. They use
individual analog front ends then multiplex the digital in a manner that is
transparent to the user.

That could be an option. Just not the Ebay path, this has to turn into a
product some day. Preferably with extra cages and backplanes.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Joerg]

krw@attt.bizz wrote:

On Tue, 25 Feb 2014 17:50:44 -0800, Joerg <invalid@invalid.invalid
wrote:

krw@attt.bizz wrote:
On Tue, 25 Feb 2014 14:01:26 -0800, Joerg <invalid@invalid.invalid
wrote:

Folks,

The AC97 standard describes only up to four sound chips operated
simultaneously, on page 21:

ftp://download.intel.com/support/motherboards/desktop/sb/ac97_r23.pdf

What if one would like to connect, say, 20 of them and all are supposed
to run nicely synchronous? Like in a digital mixer board for music.
Why AC97? There are dozens of DACs and CODECs around with all sorts
of interface options.

The goal was to use sound chips because of their attractive pricing
while offering 20+ bits of dynamic range and potentially high sample
rates. Is there another standard that comes to mind?

Sure, just about any audio DAC should work. For many channels, you'd
want something with a TDM interface. How many channels do you need?

I am not sure yet but somewhere around 30-40 audio inputs. Outputs
probably a well but inputs are more important.

I know how to roll this using individual ADCs and DACs but that gets
expensive. Plus we'll have to write our own drivers and all this fun stuff.

You'll need your own drivers anyway. ADI makes DACs up to 16
channels. I generally use Cirrus Logic 8-channel DACs (CS4385)
because they're cheaper (around a buck in volume). AKM and TI (Burr
Brown) also make some good ones.

Yes, the DAC part is probably easier because everyone has 5.1 or 7.1
chips. But only two audio-in channels per chip, usually.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Joerg]

mroberds@att.net wrote:

Joerg <invalid@invalid.invalid> wrote:
What if one would like to connect, say, 20 of them and all are
supposed to run nicely synchronous? Like in a digital mixer board for
music.

I know very, very little about this; most of what I know comes from
talking to a former co-worker who used to run a recording studio, and
recorded to hard disk in his computer. The way that it seems to work is
that you stick a PCI (or PCIe or whatever) interface card in your
computer, and then run a (probably propietary) cable from that to an
external box that actually has all the A/Ds, D/As, and clocks in it.
This external box is "doing its own thing" and is not really connected
to the audio system that lives on the motherboard. You then run
software on the computer that knows about this setup and can tell the
external box what to do - when you hit "record", the PC's main job is to
take the digital data coming from the PCI card and write it to disk.

That's the brute force approach where you end up having to build
everything and write the drivers yourself.

He used a Mac for this and had, if I remember right, the then-current
version of the "Pro Tools" software, from Digidesign (now Avid). A
quick read of the Wikipedia page suggests that at least in the past, and
possibly today as well, this software only worked with the I/O hardware
that was also sold by Digidesign/Avid.

The competitor that he mentioned was Apple's "Logic" software, but I'm
not sure which external hardware it works/worked with, or even if it
supports external hardware.

One vendor that I know of that plays in this area is Mark of the
Unicorn. I don't know if their stuff is any good or not; I just know
they exist. Their "24I/O" box seems like it might do what you want:
24 channels of 24-bit (max) inputs at 96 kHz (max). Top level at
http://www.motu.com/products/pciaudio/24IO/body.html .

Thanks! That is very interesting and there are even expansion modules if
24 channels ain't enough:

http://www.motu.com/products/pciaudio/24IO/exp.html

... The summary
http://www.motu.com/products/pciaudio/24IO/summary.html says it comes
with Windows and Mac drivers, and can sync to external time bases. The
first couple of Google hits say that a package with one of those boxes
plus the PCI card to drive it costs about US$1,420 quantity one. This
may well be beyond your budget, but it gives you some idea of what you
can have in your hands tomorrow. You then have to go and write the
software for it, but you have to do that anyway...

Standard disclaimers apply: I don't get money or other consideration
from any companies mentioned.

Thanks, Matt, that is good input. Yes, it is beyond budget but it shows
that it can be done. Plus we could buy a system from Motu as a testbed.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Joerg]

bitrex wrote:

On 2/25/2014 5:01 PM, Joerg wrote:
Folks,

The AC97 standard describes only up to four sound chips operated
simultaneously, on page 21:

ftp://download.intel.com/support/motherboards/desktop/sb/ac97_r23.pdf

What if one would like to connect, say, 20 of them and all are supposed
to run nicely synchronous? Like in a digital mixer board for music.


Here's a dirt cheap way to get a ton of analog audio inputs:

Buy one of these:

http://www.ebay.com/itm/M-Audio-Profire-Lightbridge-/201042188530?pt=US_Computer_Recording_Interfaces&hash=item2ecf0c58f2


4 ADAT lightpipe in/outs

And then get 4 of these:

http://www.soundonsound.com/sos/jun04/articles/behringerada.htm

Then you have 32 analog inputs to Firewire, all synced sample-accurate
via ADAT clock. If you need more, buy another Lightbridge and sync both
setups via their Word Cock connectors.

That looks like a good solution for a testbed. Matt had a link to Motu
where you can get 24 channels right off the bat, plus expansion modules.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Joerg]

bitrex wrote:

On 2/26/2014 2:42 PM, bitrex wrote:
On 2/25/2014 5:01 PM, Joerg wrote:
Folks,

The AC97 standard describes only up to four sound chips operated
simultaneously, on page 21:

ftp://download.intel.com/support/motherboards/desktop/sb/ac97_r23.pdf

What if one would like to connect, say, 20 of them and all are supposed
to run nicely synchronous? Like in a digital mixer board for music.


Here's a dirt cheap way to get a ton of analog audio inputs:

Buy one of these:

http://www.ebay.com/itm/M-Audio-Profire-Lightbridge-/201042188530?pt=US_Computer_Recording_Interfaces&hash=item2ecf0c58f2



4 ADAT lightpipe in/outs

And then get 4 of these:

http://www.soundonsound.com/sos/jun04/articles/behringerada.htm

Then you have 32 analog inputs to Firewire, all synced sample-accurate
via ADAT clock. If you need more, buy another Lightbridge and sync both
setups via their Word Cock connectors.

I neglected to ask if the requirement for 20+ channels of synced audio
to the computer was for a one-off installation, or was a requirement for
some kind of product that you're developing. If it's the latter I'm
curious as to what the application is, because as shown multitrack audio
recording to the PC is a completely solved problem with commodity-priced
hardware already available.

It's not a one-off but for a product. Can't talk about the application
but essentially it's the processing of electrical signals that (luckily)
happen to be spectrally in the audio band. Phase synchronicity of all
channels to each other and dynamic range are the key parameters.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Joerg]

upsidedown@downunder.com wrote:

On Tue, 25 Feb 2014 14:01:26 -0800, Joerg <invalid@invalid.invalid
wrote:

Folks,

The AC97 standard describes only up to four sound chips operated
simultaneously, on page 21:

ftp://download.intel.com/support/motherboards/desktop/sb/ac97_r23.pdf

What if one would like to connect, say, 20 of them and all are supposed
to run nicely synchronous? Like in a digital mixer board for music.

I have seen some references to 6 channel codecs intended for 5.1
systems, so you would get six synchronized channels on a single chip.
With four such chips, you would end up with 24 channels.

Anyone of those chips usable for your application ?

Not really because that's just outputs. At least all the ones I've found
never had more than two channels input.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[bitrex]

On 2/26/2014 7:39 PM, Joerg wrote:

bitrex wrote:
On 2/25/2014 5:01 PM, Joerg wrote:
Folks,

The AC97 standard describes only up to four sound chips operated
simultaneously, on page 21:

ftp://download.intel.com/support/motherboards/desktop/sb/ac97_r23.pdf

What if one would like to connect, say, 20 of them and all are supposed
to run nicely synchronous? Like in a digital mixer board for music.


Here's a dirt cheap way to get a ton of analog audio inputs:

Buy one of these:

http://www.ebay.com/itm/M-Audio-Profire-Lightbridge-/201042188530?pt=US_Computer_Recording_Interfaces&hash=item2ecf0c58f2


4 ADAT lightpipe in/outs

And then get 4 of these:

http://www.soundonsound.com/sos/jun04/articles/behringerada.htm

Then you have 32 analog inputs to Firewire, all synced sample-accurate
via ADAT clock. If you need more, buy another Lightbridge and sync both
setups via their Word Cock connectors.


That looks like a good solution for a testbed. Matt had a link to Motu
where you can get 24 channels right off the bat, plus expansion modules.

If it has to be sample accurate, I think you'll want to distribute the
word clock on coax from the master device to the slave analog input
boxes as well. There's a switch on the back of the Behringer boxes to
recover the clock from the ADAT signal, instead of using the BNC word
clock input, but IIRC it could be "sloppy."

 

On Wed, 26 Feb 2014 16:29:55 -0800, Joerg <invalid@invalid.invalid>
wrote:

krw@attt.bizz wrote:
On Tue, 25 Feb 2014 17:50:44 -0800, Joerg <invalid@invalid.invalid
wrote:

krw@attt.bizz wrote:
On Tue, 25 Feb 2014 14:01:26 -0800, Joerg <invalid@invalid.invalid
wrote:

Folks,

The AC97 standard describes only up to four sound chips operated
simultaneously, on page 21:

ftp://download.intel.com/support/motherboards/desktop/sb/ac97_r23.pdf

What if one would like to connect, say, 20 of them and all are supposed
to run nicely synchronous? Like in a digital mixer board for music.
Why AC97? There are dozens of DACs and CODECs around with all sorts
of interface options.

The goal was to use sound chips because of their attractive pricing
while offering 20+ bits of dynamic range and potentially high sample
rates. Is there another standard that comes to mind?

Sure, just about any audio DAC should work. For many channels, you'd
want something with a TDM interface. How many channels do you need?


I am not sure yet but somewhere around 30-40 audio inputs. Outputs
probably a well but inputs are more important.

With that many, the problem is getting enough TDM channels. Most DACs
only do TDM-8 so that's at least four or five channels. You're also
starting to talk about a significant amount of data. An FPGA might be
in order. What sampling rate do you need? 48kHz? 96kHz?

I know how to roll this using individual ADCs and DACs but that gets
expensive. Plus we'll have to write our own drivers and all this fun stuff.

You'll need your own drivers anyway. ADI makes DACs up to 16
channels. I generally use Cirrus Logic 8-channel DACs (CS4385)
because they're cheaper (around a buck in volume). AKM and TI (Burr
Brown) also make some good ones.


Yes, the DAC part is probably easier because everyone has 5.1 or 7.1
chips. But only two audio-in channels per chip, usually.

Four-channel CODECs are readily available. IIRC, six channel are
around, too. I find separating them to be easier, though if they're
all line level, perhaps not.

 

On Wed, 26 Feb 2014 16:53:56 -0800 (PST), Lasse Langwadt Christensen
<langwadt@fonz.dk> wrote:

Den torsdag den 27. februar 2014 01.42.23 UTC+1 skrev Joerg:
bitrex wrote:

On 2/26/2014 2:42 PM, bitrex wrote:

On 2/25/2014 5:01 PM, Joerg wrote:

Folks,



The AC97 standard describes only up to four sound chips operated

simultaneously, on page 21:



ftp://download.intel.com/support/motherboards/desktop/sb/ac97_r23.pdf



What if one would like to connect, say, 20 of them and all are supposed

to run nicely synchronous? Like in a digital mixer board for music.





Here's a dirt cheap way to get a ton of analog audio inputs:



Buy one of these:



http://www.ebay.com/itm/M-Audio-Profire-Lightbridge-/201042188530?pt=US_Computer_Recording_Interfaces&hash=item2ecf0c58f2







4 ADAT lightpipe in/outs



And then get 4 of these:



http://www.soundonsound.com/sos/jun04/articles/behringerada.htm



Then you have 32 analog inputs to Firewire, all synced sample-accurate

via ADAT clock. If you need more, buy another Lightbridge and sync both

setups via their Word Cock connectors.



I neglected to ask if the requirement for 20+ channels of synced audio

to the computer was for a one-off installation, or was a requirement for

some kind of product that you're developing. If it's the latter I'm

curious as to what the application is, because as shown multitrack audio

recording to the PC is a completely solved problem with commodity-priced

hardware already available.





It's not a one-off but for a product. Can't talk about the application

but essentially it's the processing of electrical signals that (luckily)

happen to be spectrally in the audio band. Phase synchronicity of all

channels to each other and dynamic range are the key parameters.


a good start would be to feed them all from the same oscillator, that should take care of the hardest problem, getting the sample rate exactly the same
though there might a pll for some sample rates..

PLLs aren't necessary. This isn't a huge problem at all. Digital
systems tend to be synchronous. ;-)

 

[Joerg]

krw@attt.bizz wrote:

On Wed, 26 Feb 2014 16:29:55 -0800, Joerg <invalid@invalid.invalid
wrote:

krw@attt.bizz wrote:
On Tue, 25 Feb 2014 17:50:44 -0800, Joerg <invalid@invalid.invalid
wrote:

krw@attt.bizz wrote:
On Tue, 25 Feb 2014 14:01:26 -0800, Joerg <invalid@invalid.invalid
wrote:

Folks,

The AC97 standard describes only up to four sound chips operated
simultaneously, on page 21:

ftp://download.intel.com/support/motherboards/desktop/sb/ac97_r23.pdf

What if one would like to connect, say, 20 of them and all are supposed
to run nicely synchronous? Like in a digital mixer board for music.
Why AC97? There are dozens of DACs and CODECs around with all sorts
of interface options.
The goal was to use sound chips because of their attractive pricing
while offering 20+ bits of dynamic range and potentially high sample
rates. Is there another standard that comes to mind?
Sure, just about any audio DAC should work. For many channels, you'd
want something with a TDM interface. How many channels do you need?

I am not sure yet but somewhere around 30-40 audio inputs. Outputs
probably a well but inputs are more important.

With that many, the problem is getting enough TDM channels. Most DACs
only do TDM-8 so that's at least four or five channels. You're also
starting to talk about a significant amount of data. An FPGA might be
in order. What sampling rate do you need? 48kHz? 96kHz?

48kHz would be fine. And yes, this could mean an FPGA. It would just be
nice if it doesn't have to be a total roll-our-own project.

I know how to roll this using individual ADCs and DACs but that gets
expensive. Plus we'll have to write our own drivers and all this fun stuff.
You'll need your own drivers anyway. ADI makes DACs up to 16
channels. I generally use Cirrus Logic 8-channel DACs (CS4385)
because they're cheaper (around a buck in volume). AKM and TI (Burr
Brown) also make some good ones.

Yes, the DAC part is probably easier because everyone has 5.1 or 7.1
chips. But only two audio-in channels per chip, usually.

Four-channel CODECs are readily available. IIRC, six channel are
around, too. I find separating them to be easier, though if they're
all line level, perhaps not.

There is the PCM3168 with 6-ch input, maybe that can be coaxed into a
synchronous orchestra with others.

The level can be handled via amplifiers, that's the easy part.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Joerg]

Lasse Langwadt Christensen wrote:

Den torsdag den 27. februar 2014 01.42.23 UTC+1 skrev Joerg:
bitrex wrote:

On 2/26/2014 2:42 PM, bitrex wrote:
On 2/25/2014 5:01 PM, Joerg wrote:
Folks,
The AC97 standard describes only up to four sound chips operated
simultaneously, on page 21:
ftp://download.intel.com/support/motherboards/desktop/sb/ac97_r23.pdf
What if one would like to connect, say, 20 of them and all are supposed
to run nicely synchronous? Like in a digital mixer board for music.
Here's a dirt cheap way to get a ton of analog audio inputs:
Buy one of these:
http://www.ebay.com/itm/M-Audio-Profire-Lightbridge-/201042188530?pt=US_Computer_Recording_Interfaces&hash=item2ecf0c58f2
4 ADAT lightpipe in/outs
And then get 4 of these:
http://www.soundonsound.com/sos/jun04/articles/behringerada.htm
Then you have 32 analog inputs to Firewire, all synced sample-accurate
via ADAT clock. If you need more, buy another Lightbridge and sync both
setups via their Word Cock connectors.
I neglected to ask if the requirement for 20+ channels of synced audio
to the computer was for a one-off installation, or was a requirement for
some kind of product that you're developing. If it's the latter I'm
curious as to what the application is, because as shown multitrack audio
recording to the PC is a completely solved problem with commodity-priced
hardware already available.




It's not a one-off but for a product. Can't talk about the application

but essentially it's the processing of electrical signals that (luckily)

happen to be spectrally in the audio band. Phase synchronicity of all

channels to each other and dynamic range are the key parameters.


a good start would be to feed them all from the same oscillator, that should take care of the hardest problem, getting the sample rate exactly the same
though there might a pll for some sample rates..

Feding the same clock is easy but something must make sure that the
samples are all kept in time-sync. Even when they dump their data in
sccessive order.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[miso]

Digidesign/Avid uses the Magma PCI gear I mentioned, well except for the
name on the box. They just add other software.

 

[miso]

Joerg wrote:

miso wrote:
Joerg wrote:

krw@attt.bizz wrote:
On Tue, 25 Feb 2014 14:01:26 -0800, Joerg <invalid@invalid.invalid
wrote:

Folks,

The AC97 standard describes only up to four sound chips operated
simultaneously, on page 21:

ftp://download.intel.com/support/motherboards/desktop/sb/ac97_r23.pdf

What if one would like to connect, say, 20 of them and all are
supposed to run nicely synchronous? Like in a digital mixer board for
music.
Why AC97? There are dozens of DACs and CODECs around with all sorts
of interface options.

The goal was to use sound chips because of their attractive pricing
while offering 20+ bits of dynamic range and potentially high sample
rates. Is there another standard that comes to mind?

I know how to roll this using individual ADCs and DACs but that gets
expensive. Plus we'll have to write our own drivers and all this fun
stuff.


If you don't want to roll your own cards, find a Magma PCI cage. I can
drive 7 sound cards at once on mine, well on Linux. No idea about
windows. My
Magma was from an old recording studio. I wouldn't want to pay the price
of one new, so look on ebay. And ignore all the buy it now assholes. I
got mine for about $200 plus change years ago when they were worth
something. Nowadays they have fancy multichannel soundcards. You need the
cage, backplane, and most important, the freaking PCI host cards. One
your your PC, the other in the cage. So an eight slot Magma runs 7 PCI
cards.

If you were really clever, you could build this yourself. They use
Pericom chips and off the shelf PCI backplanes. I found it easier just to
by a Magma and cheap sound cards rather than make a project out of it.
The setup is for SIGINT, so the cards works independent of each other.
But there is an opensource Linux program for multi-channel recording.

TI makes some chips that are 8 channel oversampled converters. They use
individual analog front ends then multiplex the digital in a manner that
is transparent to the user.


That could be an option. Just not the Ebay path, this has to turn into a
product some day. Preferably with extra cages and backplanes.

Windows and linux has whatever secret sauce is needed to make those PCI bus
extenders built right in. [Actually OSX as well, but I own no Apple gear so
I can't say first hand that it works on OSX.] All you have to do is make
sure the cage is powered before the PC. I really wish somebody would do an
open source project on these PCI bus extenders since they are horribly
overpriced. Worse than GPIB!

Thanks to all the ridiculous flavors of PCI these days, you don't get a lot
of PCI ports, well at least of the same type. The old PCI speed is fine for
a number of audio cards.

There are hacks you can do in Linux to make the cards start up in the same
order. That is, it can get confusing if every time you boot, the audio
inputs have reassigned themselves. I don't know about windows.

 

[Lasse Langwadt Christense]

Den torsdag den 27. februar 2014 02.29.47 UTC+1 skrev k...@attt.bizz:

On Wed, 26 Feb 2014 16:53:56 -0800 (PST), Lasse Langwadt Christensen

langwadt@fonz.dk> wrote:



Den torsdag den 27. februar 2014 01.42.23 UTC+1 skrev Joerg:

bitrex wrote:



On 2/26/2014 2:42 PM, bitrex wrote:



On 2/25/2014 5:01 PM, Joerg wrote:



Folks,







The AC97 standard describes only up to four sound chips operated



simultaneously, on page 21:







ftp://download.intel.com/support/motherboards/desktop/sb/ac97_r23.pdf







What if one would like to connect, say, 20 of them and all are supposed



to run nicely synchronous? Like in a digital mixer board for music.











Here's a dirt cheap way to get a ton of analog audio inputs:







Buy one of these:







http://www.ebay.com/itm/M-Audio-Profire-Lightbridge-/201042188530?pt=US_Computer_Recording_Interfaces&hash=item2ecf0c58f2















4 ADAT lightpipe in/outs







And then get 4 of these:







http://www.soundonsound.com/sos/jun04/articles/behringerada.htm







Then you have 32 analog inputs to Firewire, all synced sample-accurate



via ADAT clock. If you need more, buy another Lightbridge and sync both



setups via their Word Cock connectors.







I neglected to ask if the requirement for 20+ channels of synced audio



to the computer was for a one-off installation, or was a requirement for



some kind of product that you're developing. If it's the latter I'm



curious as to what the application is, because as shown multitrack audio



recording to the PC is a completely solved problem with commodity-priced



hardware already available.











It's not a one-off but for a product. Can't talk about the application



but essentially it's the processing of electrical signals that (luckily)



happen to be spectrally in the audio band. Phase synchronicity of all



channels to each other and dynamic range are the key parameters.





a good start would be to feed them all from the same oscillator, that should take care of the hardest problem, getting the sample rate exactly the same

though there might a pll for some sample rates..



PLLs aren't necessary. This isn't a huge problem at all. Digital

systems tend to be synchronous. ;-)

yes when they run off the same clock, but if you use multiple ADC each with their own PLL to do sample rates that isn't a nice fraction of the xtal rate I'm not so sure

-Lasse

 

[Lasse Langwadt Christense]

Den torsdag den 27. februar 2014 02.38.03 UTC+1 skrev Joerg:

Lasse Langwadt Christensen wrote:

Den torsdag den 27. februar 2014 01.42.23 UTC+1 skrev Joerg:

bitrex wrote:



On 2/26/2014 2:42 PM, bitrex wrote:

On 2/25/2014 5:01 PM, Joerg wrote:

Folks,

The AC97 standard describes only up to four sound chips operated

simultaneously, on page 21:

ftp://download.intel.com/support/motherboards/desktop/sb/ac97_r23.pdf

What if one would like to connect, say, 20 of them and all are supposed

to run nicely synchronous? Like in a digital mixer board for music.

Here's a dirt cheap way to get a ton of analog audio inputs:

Buy one of these:

http://www.ebay.com/itm/M-Audio-Profire-Lightbridge-/201042188530?pt=US_Computer_Recording_Interfaces&hash=item2ecf0c58f2

4 ADAT lightpipe in/outs

And then get 4 of these:

http://www.soundonsound.com/sos/jun04/articles/behringerada.htm

Then you have 32 analog inputs to Firewire, all synced sample-accurate

via ADAT clock. If you need more, buy another Lightbridge and sync both

setups via their Word Cock connectors.

I neglected to ask if the requirement for 20+ channels of synced audio

to the computer was for a one-off installation, or was a requirement for

some kind of product that you're developing. If it's the latter I'm

curious as to what the application is, because as shown multitrack audio

recording to the PC is a completely solved problem with commodity-priced

hardware already available.









It's not a one-off but for a product. Can't talk about the application



but essentially it's the processing of electrical signals that (luckily)



happen to be spectrally in the audio band. Phase synchronicity of all



channels to each other and dynamic range are the key parameters.





a good start would be to feed them all from the same oscillator, that should take care of the hardest problem, getting the sample rate exactly the same

though there might a pll for some sample rates..







Feding the same clock is easy but something must make sure that the

samples are all kept in time-sync. Even when they dump their data in

sccessive order.

I understand

could you occasionally feed all the inputs from a calibration source?
sorta like a clapper board

if you want to get fancy something like a prbs to get a nice correlation
peak

must it be done real time?

-Lasse

 

[Joerg]

miso wrote:

Joerg wrote:

miso wrote:
Joerg wrote:

krw@attt.bizz wrote:
On Tue, 25 Feb 2014 14:01:26 -0800, Joerg <invalid@invalid.invalid
wrote:

Folks,

The AC97 standard describes only up to four sound chips operated
simultaneously, on page 21:

ftp://download.intel.com/support/motherboards/desktop/sb/ac97_r23.pdf

What if one would like to connect, say, 20 of them and all are
supposed to run nicely synchronous? Like in a digital mixer board for
music.
Why AC97? There are dozens of DACs and CODECs around with all sorts
of interface options.
The goal was to use sound chips because of their attractive pricing
while offering 20+ bits of dynamic range and potentially high sample
rates. Is there another standard that comes to mind?

I know how to roll this using individual ADCs and DACs but that gets
expensive. Plus we'll have to write our own drivers and all this fun
stuff.

If you don't want to roll your own cards, find a Magma PCI cage. I can
drive 7 sound cards at once on mine, well on Linux. No idea about
windows. My
Magma was from an old recording studio. I wouldn't want to pay the price
of one new, so look on ebay. And ignore all the buy it now assholes. I
got mine for about $200 plus change years ago when they were worth
something. Nowadays they have fancy multichannel soundcards. You need the
cage, backplane, and most important, the freaking PCI host cards. One
your your PC, the other in the cage. So an eight slot Magma runs 7 PCI
cards.

If you were really clever, you could build this yourself. They use
Pericom chips and off the shelf PCI backplanes. I found it easier just to
by a Magma and cheap sound cards rather than make a project out of it.
The setup is for SIGINT, so the cards works independent of each other.
But there is an opensource Linux program for multi-channel recording.

TI makes some chips that are 8 channel oversampled converters. They use
individual analog front ends then multiplex the digital in a manner that
is transparent to the user.

That could be an option. Just not the Ebay path, this has to turn into a
product some day. Preferably with extra cages and backplanes.

Of course I meant without extra cages abnd backplanes

Windows and linux has whatever secret sauce is needed to make those PCI bus
extenders built right in. [Actually OSX as well, but I own no Apple gear so
I can't say first hand that it works on OSX.] All you have to do is make
sure the cage is powered before the PC. I really wish somebody would do an
open source project on these PCI bus extenders since they are horribly
overpriced. Worse than GPIB!

Thanks to all the ridiculous flavors of PCI these days, you don't get a lot
of PCI ports, well at least of the same type. The old PCI speed is fine for
a number of audio cards.

There are hacks you can do in Linux to make the cards start up in the same
order. That is, it can get confusing if every time you boot, the audio
inputs have reassigned themselves. I don't know about windows.

It all goes towards USB which has better standardization. USB 3.0 has
plenty of bandwidth for a gazillion audio channels. But it seems the
audio world is slow to embrace that. The RF world isn't:

http://signalhound.com/old_sh/BB60A.htm

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Joerg]

Lasse Langwadt Christensen wrote:

Den torsdag den 27. februar 2014 02.38.03 UTC+1 skrev Joerg:
Lasse Langwadt Christensen wrote:

Den torsdag den 27. februar 2014 01.42.23 UTC+1 skrev Joerg:
bitrex wrote:
On 2/26/2014 2:42 PM, bitrex wrote:
On 2/25/2014 5:01 PM, Joerg wrote:
Folks,
The AC97 standard describes only up to four sound chips operated
simultaneously, on page 21:
ftp://download.intel.com/support/motherboards/desktop/sb/ac97_r23.pdf
What if one would like to connect, say, 20 of them and all are supposed
to run nicely synchronous? Like in a digital mixer board for music.
Here's a dirt cheap way to get a ton of analog audio inputs:
Buy one of these:
http://www.ebay.com/itm/M-Audio-Profire-Lightbridge-/201042188530?pt=US_Computer_Recording_Interfaces&hash=item2ecf0c58f2
4 ADAT lightpipe in/outs
And then get 4 of these:
http://www.soundonsound.com/sos/jun04/articles/behringerada.htm
Then you have 32 analog inputs to Firewire, all synced sample-accurate
via ADAT clock. If you need more, buy another Lightbridge and sync both
setups via their Word Cock connectors.
I neglected to ask if the requirement for 20+ channels of synced audio
to the computer was for a one-off installation, or was a requirement for
some kind of product that you're developing. If it's the latter I'm
curious as to what the application is, because as shown multitrack audio
recording to the PC is a completely solved problem with commodity-priced
hardware already available.
It's not a one-off but for a product. Can't talk about the application
but essentially it's the processing of electrical signals that (luckily)
happen to be spectrally in the audio band. Phase synchronicity of all
channels to each other and dynamic range are the key parameters.
a good start would be to feed them all from the same oscillator, that should take care of the hardest problem, getting the sample rate exactly the same
though there might a pll for some sample rates..




Feding the same clock is easy but something must make sure that the

samples are all kept in time-sync. Even when they dump their data in

sccessive order.


I understand

could you occasionally feed all the inputs from a calibration source?
sorta like a clapper board

Yes, that is possible but painful because it requires extra muxes.

if you want to get fancy something like a prbs to get a nice correlation
peak

must it be done real time?

Not really but close. If there is a delay of a few seconds that's ok but
there will be signals coming in all the time, continuously.

--
Regards, Joerg

http://www.analogconsultants.com/

 

On Tue, 25 Feb 2014 14:01:26 -0800, Joerg <invalid@invalid.invalid>
wrote:

Folks,

The AC97 standard describes only up to four sound chips operated
simultaneously, on page 21:

ftp://download.intel.com/support/motherboards/desktop/sb/ac97_r23.pdf

What if one would like to connect, say, 20 of them and all are supposed
to run nicely synchronous? Like in a digital mixer board for music.

What exactly are you trying to achieve ?

Create a 20 channel audio mixer ?

Sampling some 20 discrete channels ? At what bandwidth (sampling rate)
and at what accuracy (number of bits or SNR) do you need ?

If you are doing something else than some multichannel audio
application, AC97 might not be the first choice.

At least one or two decade ago the sound cards were really bad, with
grossly incorrect sampling rate and bad temperature stability. Also
samples were frequently lost.

I tried to make a Loran-C interference eliminator (noise blanker) for
the 135 kHz band. To do so, I would have to generate clean
synchronized GRIs for each Loran-C station, so I could mute the 135
kHz receiver, each time there was a Loran-C pulse from some stations.

In initial tests, since I live quite far from a Loran-C chain, I asked
someone living closer to the Loran-C to send me some Loran-C
recordings at 100 kHz. While a local oscillator or sound card sampling
error would be quite easy to compensate, lost samples and sampling
rate wobble made it quite impossible to generate a clean version of
the GRI, thus making the GRI noise blanker quite useless.

Perhaps the sound cards are better now, but since the Loran-C is
obsolete, this is a non-issue.

 

[Joerg]

upsidedown@downunder.com wrote:

On Tue, 25 Feb 2014 14:01:26 -0800, Joerg <invalid@invalid.invalid
wrote:

Folks,

The AC97 standard describes only up to four sound chips operated
simultaneously, on page 21:

ftp://download.intel.com/support/motherboards/desktop/sb/ac97_r23.pdf

What if one would like to connect, say, 20 of them and all are supposed
to run nicely synchronous? Like in a digital mixer board for music.

What exactly are you trying to achieve ?

Create a 20 channel audio mixer ?

Sampling some 20 discrete channels ? At what bandwidth (sampling rate)
and at what accuracy (number of bits or SNR) do you need ?

Can't reveal details but it's 20+ electrical signals that spectrally
happen to be in the audio range. Several kHz. Sampling range needs to be
>40kHz and the achievable SNR should be well north of 90dB.

Afterwards the data gets heavily number-crunched in the PC.

If you are doing something else than some multichannel audio
application, AC97 might not be the first choice.

I already did something similar with AC97 but that only needed two input
channels and one output channel. Now I need more, a lot more.

At least one or two decade ago the sound cards were really bad, with
grossly incorrect sampling rate and bad temperature stability. Also
samples were frequently lost.

I tried to make a Loran-C interference eliminator (noise blanker) for
the 135 kHz band. To do so, I would have to generate clean
synchronized GRIs for each Loran-C station, so I could mute the 135
kHz receiver, each time there was a Loran-C pulse from some stations.

In initial tests, since I live quite far from a Loran-C chain, I asked
someone living closer to the Loran-C to send me some Loran-C
recordings at 100 kHz. While a local oscillator or sound card sampling
error would be quite easy to compensate, lost samples and sampling
rate wobble made it quite impossible to generate a clean version of
the GRI, thus making the GRI noise blanker quite useless.

Perhaps the sound cards are better now, but since the Loran-C is
obsolete, this is a non-issue.

I found sound card performance stellar so far, even for the ones on my
older Samsung NC10 or the Durabook 14. Using the Daqarta tool kit I was
able to reliably and most of all repeatably measure phase shifts of
fractions of a degree.

--
Regards, Joerg

http://www.analogconsultants.com/

 

On Wed, 26 Feb 2014 17:35:40 -0800, Joerg <invalid@invalid.invalid>
wrote:

krw@attt.bizz wrote:
On Wed, 26 Feb 2014 16:29:55 -0800, Joerg <invalid@invalid.invalid
wrote:

krw@attt.bizz wrote:
On Tue, 25 Feb 2014 17:50:44 -0800, Joerg <invalid@invalid.invalid
wrote:

krw@attt.bizz wrote:
On Tue, 25 Feb 2014 14:01:26 -0800, Joerg <invalid@invalid.invalid
wrote:

Folks,

The AC97 standard describes only up to four sound chips operated
simultaneously, on page 21:

ftp://download.intel.com/support/motherboards/desktop/sb/ac97_r23.pdf

What if one would like to connect, say, 20 of them and all are supposed
to run nicely synchronous? Like in a digital mixer board for music.
Why AC97? There are dozens of DACs and CODECs around with all sorts
of interface options.
The goal was to use sound chips because of their attractive pricing
while offering 20+ bits of dynamic range and potentially high sample
rates. Is there another standard that comes to mind?
Sure, just about any audio DAC should work. For many channels, you'd
want something with a TDM interface. How many channels do you need?

I am not sure yet but somewhere around 30-40 audio inputs. Outputs
probably a well but inputs are more important.

With that many, the problem is getting enough TDM channels. Most DACs
only do TDM-8 so that's at least four or five channels. You're also
starting to talk about a significant amount of data. An FPGA might be
in order. What sampling rate do you need? 48kHz? 96kHz?


48kHz would be fine. And yes, this could mean an FPGA. It would just be
nice if it doesn't have to be a total roll-our-own project.

I think if you want to do it for a reasonable price, it's going to go
that way.

I know how to roll this using individual ADCs and DACs but that gets
expensive. Plus we'll have to write our own drivers and all this fun stuff.
You'll need your own drivers anyway. ADI makes DACs up to 16
channels. I generally use Cirrus Logic 8-channel DACs (CS4385)
because they're cheaper (around a buck in volume). AKM and TI (Burr
Brown) also make some good ones.

Yes, the DAC part is probably easier because everyone has 5.1 or 7.1
chips. But only two audio-in channels per chip, usually.

Four-channel CODECs are readily available. IIRC, six channel are
around, too. I find separating them to be easier, though if they're
all line level, perhaps not.


There is the PCM3168 with 6-ch input, maybe that can be coaxed into a
synchronous orchestra with others.

The level can be handled via amplifiers, that's the easy part.

My point was that depending on the power level needed, separate DACs
and ADCs can be easier than CODECs (keeping the ADCs away from power
amps).