On Mon, Aug 02, 2010 at 02:10:56PM +0200, Remco wrote: > I was looking at the Alesis iO|2 USB audio interface. It seems like a nice > device, especially since it appears to comply to both the USB-audio as well > as the USB-MIDI standard, see: > http://www.linuxquestions.org/ > questions/linux-hardware-18/2-soundcards-alesis-io|2-and-nvidia-ck804-512025/ > > However, it appears to limit audio to 24-bits @ 44.1/48kHz. > > To my understanding, applications accessing this device > through libsndio will use its native resolution. For > applications requiring 16-bit audio I could run > an aucat server on top of this device.
yes > According to BUGS in aucat(1), aucat uses 16-bit > processing. Does that mean that aucat will always > record/playback only the 16 most significant bits for > resolutions > 16 bit (always limiting the dynamic range) ? yes > Apart from limiting the dynamic range, I was wondering if > a pure 24-bit device could potentially be troublesome in > any way. e.g. will running an aucat server in 16-bit mode > add any kind of additional distortion or noise, or can i > expect it to behave as a device doing 16-bits @ 44.1/48kHz > ? The trunctation of least significant bits is equivalent to around -96dB noise. This is not far from what mixers, preams, cables, etc generate. The aucat resampler generates a slightly audible noise, so it shouldn't be used when recoring if quality is important. I'd recommend, completely avoiding resampling by using a common sample rate for all recordings and/or resampling off-line at the end. so, yes, aucat is equivalent to a 16-bit device as long as it's not resampling. > Will applications work without issues ? The fact that the device supports 24-bit encodings only won't cause compatibility problems, I use envy(4)'s for everything audio-related, and it's 24-bit only too. Most programs should work as long as aucat is running. Support of 24-bit encodings and usb 2.0 in the uaudio driver are recent, and I don't know how much is still to do. Jacob may give hints about that. -- Alexandre
