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I have seen the likes of M-Audio fast track and similar devices that somehow covert an analogue voltage audio signal to a digital data stream which you can connect via USB to your computer. If I open something like Garageband it just appears as another input without any special configuration. I am interested in building my own.

An example application would be; record guitar onto a computer software e.g. Garageband, Logic Pro etc.

I understand that there is a ADC (Analogue to Digital Converter) which will convert the analogue audio levels to digital.

What I am trying to figure out is, how does this interface with the computer?

All of these devices seem to work without needing specific drivers and such so, there I'm guessing there may be a specific protocol they all follow? I can't seem to find something exact.

If there is a protocol that they follow, does anyone have any info or any idea about this? Is this the same universal protocol that is used by the likes of USB audio speakers etc? Is this similar to SPDIF and the like? Is this conversion from output of ADC to USB data stream something which we can do, say, with a microcontroller?

I know that its much easier just to build an analogue preamp or the like to connect it to the audio input port on a PC but as I said, I am interested in how they make the USB interface.

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  • \$\begingroup\$ I've got an old analogue input usb thing but it needed an install to enable it to work. \$\endgroup\$
    – Andy aka
    Commented Jun 1, 2013 at 14:32

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universal protocol that is used by the likes of USB audio

Sounds like the USB Audio Class specification.

Is this conversion from output of ADC to USB data stream something which we can do, say, with a microcontroller?

Some USB microcontrollers - NXP LPC17xx for example - have example code for USB Audio Class available.

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  • \$\begingroup\$ Cheers! After some research, it seems like a lot simpler than I thought. I had in mind a variety of different formats and things which would be hard to interface together. Atleast these USB audio interfaces all use this "USB Audio" class I think. Which is why they don't need drivers! \$\endgroup\$
    – midnightBlue
    Commented Jun 1, 2013 at 19:16
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    \$\begingroup\$ Nitpick mode: they do need drivers, but due to their generic nature most OSes readily include them in the standard distribution. Many professional audio interfaces will work with the "standard" drivers from the OS, but also come with a custom device driver to control certain aspects of the device and/or achieve lower latency. \$\endgroup\$
    – Mels
    Commented Sep 26, 2013 at 11:53
  • \$\begingroup\$ For instance, Windows still doesn't include support for USB Audio Class 2.0, even though it's been standardized since 2006, so devices with more than 2 channels need drivers on Windows but not on any other OS. \$\endgroup\$
    – endolith
    Commented Mar 18, 2016 at 18:15
  • \$\begingroup\$ @endolith it seems USB audio class 2 is now supported on Windows 10. I have not tested it though. \$\endgroup\$
    – bobflux
    Commented Mar 24, 2018 at 17:51

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