USB Audio confusion - What data rates are possible?

Asked Mar 20 '14 at 13:12

Active Mar 20 '14 at 13:12

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I'm new to USB development, and i'm quite confused about what data rates are realistic.

I'm trying to develop an external sound card connected on an AVR32 processor, which supports USB Full Speed(12 Mb/s). I'll use USB audio class 1 to send the audio data to a PC. I need to send 24 bit, 48kHz, 2 channels as INput to the computer, but also 24 bit, 48kHz, 1 channel OUTput from the computer. Streaming both ways.

That gives me a data rate of: 24 bit * 48kHz * 3 channels = 3,5 Mb/s, which should be possible by using USB Full Speed?

I understand that the Audio Class sends data via an Isochronous transfer, but i'm confused about how many transactions ( e.g. IN = 256 bytes ) it is possible to make in one frame? according to the USB specification (http://www.usb.org/developers/docs/usb20_docs/#usb20spec - > table 5-4) it seems to be possible to send more than one transaction per frame?

Is it possible to send both IN and OUT packets within one frame?

Thanks in advance!

asked Mar 20 '14 at 13:12

Wiingaard

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It's actually 4.3Mb/s assuming that the audio data is packed. If not, 5.6Mb/s. – marko Mar 20 '14 at 21:26
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How do you get those number.? – Wiingaard Mar 24 '14 at 07:57
24-bite = 3 bytes * 3 channels * 48kHz = 4.32Mb/s. Of course, you have framing to add to this. – marko Mar 24 '14 at 08:25
Hmm, i get: 3 bytes * 3 channels * 48kHz = 3.45 Mb/s = 0.432 MB/s – Wiingaard Mar 24 '14 at 11:18

USB Audio confusion - What data rates are possible?

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