Sun, 6 Apr 2014 06:23:37 +0100, Dave Malham <[email protected]> wrote :
> Lets not worry too much about silicon - it's ridiculously cheap these > days, so long as you are not going for the top end. If we are to use > cheap, ready built, USB units and not our own purpose built kit (and > that's not unthinkable, this is the age of the maker, right?) I think > it all hinges on two things, synchronisation and bit rate. For 24 > bits and 48 Khz, which is, I guess, about the lowest we'd all be > happy with, that's 1152 kilobits per second, which means for USB 2, a > practical limit of 8/10 channels per plug, all things being equal. > This is why there are 7.1 units out there. Hi Dave. The previously mentioned cheap USB sound modules are limited to 16 bits and 48Khz. When resampling 24bit sources with dithering, 16 bits is enough for domestic use. At 48Khz, that's 768Kbps per channel, and at 44.1Khz that's 705.6Kbs. So the required USB bus speed for 8 channels is 6144Kbps or 5645Kbps (maybe more with some protocol overhead). These modules work with USB 1.1, not USB 2. The USB 1.1 standard have two speeds: low at 1.5Mbps, and full at 12Mbps. So, theoretically, a single USB 1.1 bus at full-speed can handle two 7.1 sound modules at 16bit/44.1Khz. I don't know how a USB 2 hub deal with several USB 1.1 devices. I yet have to test two modules with a RPI. -- Marc _______________________________________________ Sursound mailing list [email protected] https://mail.music.vt.edu/mailman/listinfo/sursound
