I was thinking of designing a multichannel usb soundcard.
If I will be successful, then the soundcard will have opensource drivers,
and I will make sure that it works well with Audacity on both linux and windows.
I already have a pretty good idea about the ADCs, and the controller that I will use.
What I would like to know is a couple of things that you guys would like to see in a multichannel sound card.
Please respond to any of the following questions that you would be interested in:
Minimum number of inputs?
Preferred number of inputs?
Number of line-level vs. microphone/preamplified inputs?
Preferred Input connector type? (for example RCA,XLR,TRS(2.5/3.5/6.36mm?), something else?)
Should they be simple mono inputs? balanced differential inputs? inputs that can be connected directly to the ‘insert’ ports of a mixer, using stereo TRS cables?
Do you need configurable sampling rate, or is it okay to hardcode it to a maximum of 192kHz?
Do you need input gain adjustment on all channels, or can you live without it?
Would direct recording to SDcard(s) be useful?
Do you need outputs? Do you need the same number of outputs as inputs?
I was thinking of designing a multichannel usb soundcard.
Why?
Do you have the equipment to test a microphone amplifier? How about dual-tone intermodulation testing? RF Suppression – Part 15 certification in the US?
Past the design problems, you’re going to spend a year or two performing all the driver evaluations – and then hope the next OS Updates don’t make you start all over. Multi-channel is not natively supported on any platform I know of.
That and the two of us on Macs are really excited you decided to leave us out.
2) Preferred number of inputs?
More would be nice, but I’d expect performance problems and a steep increase in price. I’d be happy with 8.
3) Number of line-level vs. microphone/preamplified inputs?
Minimum 2 x microphone (XLR) with optional phantom power (preferably individually selected).
Mic/Line level preamps for all channels would be nice, but there’s a cost/quality trade-off. More than 2 good quality mic inputs is likely to be too expensive.
4) Preferred Input connector type? (for example RCA,XLR,TRS(2.5/3.5/6.36mm?), something else?)
XLR/Jack hybrid for first 2 channels.
1/4" balanced jack (unbalanced compatible) for all other channels.
5) Should they be simple mono inputs? balanced differential inputs? inputs that can be connected directly to the ‘insert’ ports of a mixer, using stereo TRS cables?
See 4.
6) Do you need configurable sampling rate, or is it okay to hardcode it to a maximum of 192kHz?
44.1 and 48 kHz.
7) Do you need input gain adjustment on all channels, or can you live without it?
Gain adjustment required on Mic inputs.
8) Would direct recording to SDcard(s) be useful?
Don’t care.
9) Do you need outputs? Do you need the same number of outputs as inputs?
Minimum 2 channel outputs. If I was using this “portable” I would not want to carry a separate output device.
4 output channels would be nice. Although Audacity does not currently support more than 2 output channels, it would be useful for other applications or when using Jack Audio System.
10) Other features?
Affordable.
Full clock synchronisation between channels. There must be no drift in sample rate between channels.
Full multichannel device driver - both Audacity and Jack only support one input device.
Must support Jack Audio System.
Preferably 24 bit A/D.
Optional: Channel router application so that any physical input can be routed to any software input channel. This can already be done with Jack Audio, but it would be useful for other systems to be able to (for example) route Inputs 7 and 8 through to Audacity input channels 1 and 2.