There seems to be some confusion about USB audio connections and what works with what etc. I'm going to try and clarify this and explain how these relate to the EDO applet.
There are two speeds that USB DACs can run at: full speed and high speed. Full speed: 12 mega bits (Mb) per sec. Max sample rate is 96KHz. High speed: 480Mb/s, supports 192KHz and up. There are two generic "protocols": USB Audio Class (UAC) 1.0 and UAC 2.0 UAC1.0 was the original which came out before high speed mode was invented, thus it does not support high speed mode, thus it is limited to a max 96KHz sample rate. UAC2.0: supports both full speed and high speed, DOES support 192 (but only at high speed), multi channel etc. All DACs that use UAC2.0 do so in order to run at high speed and support 192. Some of these will "downgrade" to UAC 1.0 and full speed if the DAC is plugged into a computer that does not support UAC2.0 There are two "modes" in common use: adaptive and asynchronous. In adaptive the DAC has to change the frequency of its internal clock to match the average data rate of whats coming over the USB bus. In asynchronous the DAC uses a fixed frequency clock and tells the computer to slow down or speed up the data transfer rate. Asynch can theoretically sound better. Any particular DAC will have a mix of these. There are some combinations that don't seem to get built: all the implementations I know of that use UAC2.0 are also Async, and I don't know of any DACs that run UAC2.0 and just full speed. Async can exist in both UAC1.0 and UAC2.0. So how does this relate to EDO? There seems to be a bug in the Touch hardware that prevents async from working properly when running at full speed. In this case you need the USB 2.0 hub which talks to the Touch at high speed, but talks to the DAC at full speed. This gets around the bug in the Touch. This is only needed for an async full speed DAC. An adaptive full speed DAC or a high speed DAC of any type can be used without the hub. Thus if your DAC is a full speed only DAC (ie has a maximum sample rate of 96KHz) and you get ticks and pops, it is probably running using async mode and will need the hub to work properly. Any other DAC does not need the hub to work properly. But should still work even if you do use a hub. Thus if your DAC supports 192, you do not need the hub. If your DAC only goes up to 96KHz, it may or may not need the hub. In all these cases the DAC must be plugged into the Touch and turned on before the Touch is booted. This process will tell the server what the maximum sample rate of the DAC is, thus it should automatically downsample in the server only if the DAC does not support the sample rate. (of course this assumes that the DAC is honest about what it tells the Touch) Now just to complicate things a little bit, EDO supports a "work around" that will let SOME full speed async DACs to work with out a hub, but in this case it ONLY works for 44.1 and 48KHz. Most people are probably better off not even thinking about this and just use the hub. In addition to all this USB stuff EDO includes a new S/PDIF driver that will go up to 192. This is completely sperate from the USB stuff, but Triode was playing with the driver and wanted to get it to run at 192, so he included it in EDO. I hope this helps a little in clairifying things. John S. ------------------------------------------------------------------------ JohnSwenson's Profile: http://forums.slimdevices.com/member.php?userid=5974 View this thread: http://forums.slimdevices.com/showthread.php?t=94512 _______________________________________________ Touch mailing list [email protected] http://lists.slimdevices.com/mailman/listinfo/touch
