[linux-audio-user] [USB audio capture]: "standard" drivers, "mixers" and level controls

[Clemens Ladisch]

Mannr at uwaterloo.ca wrote:
> 1. Is there a "standard" USB interface for audio?

Yes. This is the reason why there is one driver (snd-usb-audio) for
all kinds of USB audio devices. (If you're curious, the specifications
are available at <http://www.usb.org/developers/devclass_docs>.)

> For example, will newer devices, like "Audiophile", "MobilePre",
> and "Transit" from Maudio work using some kind of standard
> interface as the "Duo" and "Quadro"?

The newer M-Audio devices are compatible to the USB Audio
specification after the driver has loaded a device-specific firmware
into them. Such a loader doesn't yet exist for Linux.

> I've seen references to "ASIO" or somesuch.  Does that mean they
> will all function with standard drivers?

ASIO is a driver architecture introduced by Steinberg to overcome the
limitations of Microsoft's MME architecture from Windows 3.x.
It isn't relevant to Linux.

> 2. What do the [alsa|au|x]mixer controls do?

ALSA simply exposes the controls of the hardware, so the
number/type/meaning of the mixer controls depends entirely on the
capabilities of the device.

> I could not find this information, neither in docs from Maudio nor in alsa
> docs.  Please point me to the appropriate place if this is written down
> somewhere.  What I am looking for is a "block diagram" showing where
> the amps and level controls really are.

You'd have to ask M-Audio for this (or other M-Audio users).

> Or, perhaps some devices have mixers, but USB control code is not written?

The USB Audio specification defines the mixer interface, too, so this
shouldn't be a problem.


HTH
Clemens