USB audio codec with SPDIF or I2S out - diyAudio
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Old 11th June 2005, 09:48 AM   #1
bocka is offline bocka  Germany
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Question USB audio codec with SPDIF or I2S out

Did anyone know a USB audio codec which has a SPDIF or I2S output? I know the PCM2902 but are there other chips? I'd prefer 24 bit and 96 kHz samplingrate if possible.
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Old 14th June 2005, 08:59 AM   #2
bocka is offline bocka  Germany
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Has really no one an idea?
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Old 14th June 2005, 09:16 AM   #3
matjans is offline matjans  Netherlands
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ti only has 48kHz 16bit stereo audio codecs with usb functionality on-chip.
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Old 14th June 2005, 09:23 AM   #4
bocka is offline bocka  Germany
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Hi matjans,

thank you. I think there should be chips with higher datarates and resolution available as there are USB soundcards with 96 kHz and 24 bit on the market.
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Old 14th June 2005, 10:30 AM   #5
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Unfortunately 96 kHz and 24 bit chips does not exist AFAIK. All the soundcards 96/24 use custom solutions, and require drivers, with all the complications that this involves.
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Old 14th June 2005, 10:40 AM   #6
matjans is offline matjans  Netherlands
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well of course there are, ti just doesn't have them as all-on-chip variants... Get a separates, build a board, write a driver and that's it ...

afaik, the standard usb audio drivers included with windows (nt, 2k, xp whatever) only support data rates up to 48kHz, 16 bits. (somebody please prove me wrong)
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Old 14th June 2005, 10:46 AM   #7
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This is not really an answer to your question but M-audio produces a cheap USB Audio Interface (24bits 96kHz) called Transit I don't know what chip they are using. You can use this little interface as a start. Red Wine Audio do some mods on this unit to transform it into there USB select unit.
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Old 14th June 2005, 11:29 AM   #8
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..actually, the PCM2902/6 works also at 96 kHz, also up to 100 kHz. But its bandwidth is limited to 24 kHz. Here are some loopback tests done on a soundcard that I designed, based on the PCM2902/6.
(PCM2902 and PCM2906 are basically the same chip)

The bandwidth is obtained from the FFT of the loopback impulse response.

Loopback at 48 kHz:
Click the image to open in full size.
(click to enlarge)


Loopback at 96 kHz:
Click the image to open in full size.
(click to enlarge)

The bandwitdth limit is visible and measurable


I checked the SPDIF output of the PCM2906 at 96 kHz, full of hopes.. but it is limited to 48 kHz:

Click the image to open in full size.
(click to enlarge)

The SPDIF out from the PCM2906 has been analized using the digital input of another soundcard (by RME) that allows to analyze the incoming digital data
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Old 15th June 2005, 08:54 AM   #9
bocka is offline bocka  Germany
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Quote:
Get a separates, build a board, write a driver and that's it
Yes, I know using a generic USB device controller and writing some lines of code can support anything I'm looking for. Unfortunately it takes some month of work...

I just took a look to the Cypress CY7C6801x series. Seems to be possible when using an additional FPGA.

Quote:
checked the SPDIF output of the PCM2906 at 96 kHz, full of hopes.. but it is limited to 48 kHz:
Interesting that it works at least. Maybe the driver itselves limits the datarate to 48kHz?
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Old 15th June 2005, 09:31 AM   #10
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Quote:
Originally posted by bocka


Interesting that it works at least. Maybe the driver itselves limits the datarate to 48kHz?
I'm more inclined to think that is a limit in the firmware on the chip..
But don't have a final word.
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