Real-time audio recording, looping, mixing

Question

From what I've read, it is possible to record audio using an external USB soundcard or a USB webcam. But everything I've seen so far is just concerned with recording sound and saving it. What I'd like to do is imitate a multi-track sequencer, does anyone know if this is already possible?

What I mean is, you press a key and start recording your "B ts B tsts B ts", then press another key and it plays back this track in a loop. Then, while this track is playing, you press another key and record the "dom dom dom dom" over the top. Finish this one and it now plays both these tracks together in an infinite loop. Then maybe temporarily mute the first track while you sing the "la la la la" and then unmute the first track again. I don't want to carefully prepare and arrange and program these tracks to produce some finished output, I just want to play with it in real-time. So that means playing and recording simultaneously, playing multiple sound elements simultaneously, and not relying on some kind of offline slow processing.

Now maybe this kind of thing is already available for the pi and I just have to install it, or maybe it's the kind of thing which pygame could do relatively easily if I just have to put the pieces together. It would have to be low latency though, it wouldn't work if there were awkward pauses at the end of the loops. Or maybe the pi just isn't a suitable platform for this?

Answer 1

Since no one has responded to this in 3 months, and I've found this post researching a similar question I would like to put my 2 cents in:

Audacity is an open-source program that works on Linux and can do most of what you have described running on a desktop.

This Page from the R-Pi forum looks like a good starting place. That's where I'm going to continue my research.

I have not tried Audacity on the pi myself, however others have experienced some issues. I suspect you will run into problems with any program you find for the following reasons.

Processing audio real time requires a significant amount of system resources (RAM and CPU), There is plenty of examples of the pi being able to record and save audio. However USB 2.0 has significantly slower data transfer rates than SATA or IDE, saving audio while playing back multiple tracks will most likely exceed that rate unless you are using a very low sample rate for your recording which would result in poor audio quality.

A program might be able to circumvent this limitation by keeping those recordings in the RAM, which would be limited to the UN-expandable 512MB installed on the the Pi-B. This could work for short clips or compressed audio.

I would be pleasantly surprised if there is a program out there that can work within these limitations. I have seen live performances that use specialized audio looping equipment for this purpose. It would really neat if you could make one of these devices using a Pi.

I hope that you get a better answer to this question, if you have found an answer since you posted the question I would be interested in knowing your solution. Good Luck!