[LAD] Is there a Linux Software Mixer?

[Rory Filer]

Hi All

I think I know the answer to this, but I was wondering if it's
possible to mix two separate audio sources in software. I'd like to be
able to play announcement-type audio atop the currently playing main
track. An example might be when driving down the Autobahn and a
traffic report temporarily pre-empts whatever it is you are listening
to. In my case, though, I'd prefer to keep the main audio playing, but
at a very low volume level compared to the short announcement..

My setup is a roll-your-own embedded Linux distro with kernel 2.6.28.
I'm using Alsa SoC audio driving an I2S output on my Marvell processor
(which is now working just fine, BTW). The I2S signals feed an FM
transmitter chip which is broadcasting audio to a nearby FM receiver.
The FM chip only has the one input so no mixing possible within that
part. Anyhow, considering I only have a single I2S output, seems to me
that I'd need to do the mixing somewhere upstream of that serial port
within the Linux machine. But there is no special hardware for this
and I think the answer is "no, there is no way to mix two separate
audio tracks without a DSP and another device driver". But I thought
I'd ask just the same.

Regards,

Rory