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In Reply to: Re: You should read up on audio USB posted by Scrith on July 7, 2006 at 19:56:46:
A few words on USB audio formats:
all USB audio modes are isochronous, this means that the bandwidth for the audio data is reserved on the bus so resource allocation doesn't have to be renegotiated for every packet of data sent. Synchronous, adaptive and asynchronous are all isochronous modes, the host sends packets out at a regular rate (thats what isochronous means, constant time). For the first two the receiving end has to match the host's data rate, for asynchronous the device can tell the host to slow down or speed up to match the rate its using the data.In none of these cases does it work like an ethernet with handshaking on each packet where the receiver requests a packet when it needs one. When the pipe is setup the host and device negotiate a speed and the host starts spewing out packts, its up to the device to keep up. In asynchronous the device can tell the host to change the data rate on the fly, thats the only difference.
Note that there is no error correction or retry on bad data. There is a simple error detection mechanism sent, but no means to retry if there is an error, you can flash a light on the front pannel but thats about it. Someone calculated that for a system that is within the USB specs an error should occur an average of once every 4 months or so for a system running 24 hours a day. The spec writers did not think this was important enough to spend the extra bandwidth and messiness on error recovery methods for audio.
John S.
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Follow Ups
- USB audio modes - John Swenson 09:50:03 07/08/06 (0)
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