10-chan sound card 5x pcm2906?

[DragonMaster]

I plan on building a "soundcard" with 10 channel inputs.

Would 5x PCM2906 at the same time on one USB port using an hub work or there's too much bandwidth?

Also, I plan using some OPA4134 as opamps. Is there a need for them anyways?

[paologatto]

Supposing to connect the 5 PCM2906 to 5 different USB ports (this is the only way for overcoming the bandwith limit), you will have 5 different USB soundcards, with different clocks (no sync between them, also at same sample rate), and all named by the PC "USB device". How to distinguish the channels?

[DragonMaster]

and all named by the PC "USB device". How to distinguish the channels?

Connect a 24C01 EEPROM to each of them to change their device name.

5 ports? I guess I could use less ports than that. Some people connect two PCM2906 in a hub and it works.

And, also, every pair of USB ports on the PC are 1 port with 2-port hubs.

If there's too much bandwidth needs, I could connect an USB2 hub to an USB port I think, no?

[paologatto]

Originally posted by DragonMaster


Connect a 24C01 EEPROM to each of them to change their device name.

Really? I though that the descriptor on the PCM2906 could be modified only by the manufacturer. Maybe I'm wrong.
Can you give more details about this procedure?

Originally posted by DragonMaster


5 ports? I guess I could use less ports than that. Some people connect two PCM2906 in a hub and it works.

Well, since all my computers are old and have only USB1.x ports, I have tested only attaching different PCM2906 based soundcards on different ports. It works, although I tested with only 2 simultaneous soundcards.
My doubts were about the sync between each them (remember that there is also the SpAct..) but I just tested recording with a multitrack recording software on different PCM2906 USB soundcards from a single signal generator and after 5 minutes the recorded tracks were still in sync.. so this test is promising for a PCM2906 based multichannel soundcard.

[DragonMaster]

Oh, sorry, about the EEPROM, it's only for the PCM2706.
I will ask TI for "chaging the device ID". That what they tell to do in the datasheet.

I've heard cases like two different sound cards have a 1 seconds delay after 1 week.

I don't know if SpAct is working only if there is no external clock connected. If it works also with an external clock, maybe it's syncing the external signal with it.

[gmarsh]

Just think of the PCM2906 as a CS8416, which decodes a USB audio stream instead of an IEC958 stream - the computer pushes audio at the part, which accepts this data and recovers a clock from it. SpAct is TI's clever PLL architecture for doing the recovery.

Assuming that your OS sends audio packets to each of your PCM2x0x parts at the same rate, you shouldn't get any "slip" occuring.

[DragonMaster]

Thanks for the answers. I guess the only way to know if it will work is to try! TI doesn't specify the amount of b/w it requires.

Maybe 1600kpbs as a 16-bit 44.1kHz CD is working @ 1450kbps?
But, 1600 x5 is 8mpbs, and USB1.1 is 12MB.

But if USB is half-duplex, I will not be able to play and record at the same time, since there will be 8MBs of upload and 8MBs of download. I don't have any USB2 ports, so either a USB2 card or multiple ports with the same number of cards would be requiered.

[paologatto]

The PCM2906 is perfectly full-duplex. The problem is only the bandwidth of the USB1.x
One way stream of audio data (considering only audio data and not other additional info) is:

44,1 kHz sample rate / 16-bit samples / 2 audio channels = 1.4 Mbps

1 USB soundcard Full duplex @ 44.1 kHz = 2.8 Mbps

USB 12 Mbps / 2.8 = 4.2 soundcards

But there are also other data transmitted and the USB bandwidth most probably will be less than 12 Mbps, so 2-3 full-duplex soundcards can be used but not much more with USB 1.x

Using an USB2 port, it must be checked that the USB2 port will not go automatically in 12 Mbps mode when a USB 1.x device is attached. Maybe a smart hub can share correctly the USB2 bandwidth to give to many PCM2906 soundcards the right bandwidth..

[DragonMaster]

that the USB2 port will not go automatically in 12 Mbps mode

Do you mean 200mpbs?

Maybe it does, you can connect more "low-speed" mode devices in a USB1.1 port than "full-speed" ones.

But there are also other data transmitted and the USB bandwidth most probably will be less than 12 Mbps, so 2-3 full-duplex soundcards can be used but not much more with USB 1.x

16-bit 48khz eats even more bandwidth.


I think all hubs are "smart", if you go in a device's USB proprieties in Window$, it will show how many % of the total speed is being used by the device. It tell an hub normally requires 10% of the bandwidth. Quite a lot imo. A USB2 card is 10$ so I guess I could give it a try! I'll get an hub chip from TI.