Which software player do you like?

[Vincent Kars]

Currently all major OS support USB audio 1 standard. This is limited to 24/96.
A lot of implementations are limited to 16/48 simply because this can be done using a cheap drop in USB receiver.
Early 2009 the USB audio 2 specs where finalized. This supports 174/196.
As far as I know, there are no native mode audio drivers at the present supporting USB audio 2.
32 bits is not supported by this standard but I don't think there are audio files using more than 24 bits.
24 allows for a dynamic range of 144 so -144 dBFS, well below the noise floor of any gear.

[dave2010]

Currently all major OS support USB audio 1 standard. This is limited to 24/96.
A lot of implementations are limited to 16/48 simply because this can be done using a cheap drop in USB receiver.
Early 2009 the USB audio 2 specs where finalized. This supports 174/196.
As far as I know, there are no native mode audio drivers at the present supporting USB audio 2.
32 bits is not supported by this standard but I don't think there are audio files using more than 24 bits.
24 allows for a dynamic range of 144 so -144 dBFS, well below the noise floor of any gear.

Interesting about the current 24/96 USB. Presumably that affects some manufacturers - e.g Stan - so one upgrade he could do is to fit 24/96 USB on the next generation Caiman. It also seems likely that bottom end computers would now have the 16 bit limit not for any particularly good technical reason, but simply to differentiate them from middle and high end kit. I shall look out for a 24 bit audio interface on the next computer I buy. [Does the iMac have 24 bit USB audio?]

24 bits should normally be more than enough for high quality audio - you are right about the noise floor etc. However, I think I could see a use for 32 bit floating point - though maybe it's a bit dubious. It'd still be 24 bit data, but level changes would be easy, could be done digitally. Obviously it should be possible to convert between 24 bit integer and 32 bit floating point without too much difficulty. It might be easier to make a digital mixing desk to work with floating point.

I found the USB audio 2 spec documents, but I couldn't find anything about the rates allowed. I take your word for it that they go up to 196 kHz. There could be some issues about sampling rate conversion - as we noted earlier. The spec does permit SRC to be done in some fairly flexible ways I think, at a quick glance. Most of the time end users should be happy enough with 96kHz or lower rates, but it's always possible that some will detect better quality at higher rates - possibly due to side effects, rather than theory.

[Vincent Kars]

It also seems likely that bottom end computers would now have the 16 bit limit not for any particularly good technical reason, but simply to differentiate them from middle and high end kit. I shall look out for a 24 bit audio interface on the next computer I buy. [Does the iMac have 24 bit USB audio?

If you talk USB audio, all PC/iMac support 24/96 simply because that is the USB 1 audio standard and their native mode USB audio drivers adhers to this standard. Most outboard DACs are not capable to use this simply because of the USB receiver chip they use as mentioned above.
So this is not a limitation of the PC but of the (outboard) DAC
Bit more detail: http://thewelltemperedcomputer.com/KB/USB.html

[dave2010]

vincent

Thanks again.

If you talk USB audio, all PC/iMac support 24/96 simply because that is the USB 1 audio standard and their native mode USB audio drivers adhers to this standard. Most outboard DACs are not capable to use this simply because of the USB receiver chip they use as mentioned above.
So this is not a limitation of the PC but of the (outboard) DAC
Bit more detail: http://thewelltemperedcomputer.com/KB/USB.html

So we really do need to talk to our friendly DAC manufacturers about this then. Not quite sure what the point of having the audio at 24/96 is if it can't drive an external DAC, and using another computer as an external soundcard doesn't make too much sense either.