Ok, so I’ve recently had to deliver some files to a client for their IVR phone systems; i.e., the stuff you hear while you’re on hold. It has been most troublesome finding software that will actually hack it down to 8-bit, since no one really cares about 8-bit audio anymore (except people using these systems). After trying many things, SRC and dithering with Izotope RX (arguably the highest quality software to use for SRC), I found that the result was acceptable, though noisy from the dithering, not to mention that I still ended up with a 16-bit file. Audacity kind of worked, but I had to go get an old version to make it 8-bit.
What ended up working the best by a large margin was actually sox. I did it on linux, but it appears it’s cross-platform. I fed it 48kHz, 16-bit wav files, and let it do its work. It ended up being super clean and encoded perfectly.
Here’s a script that you can drop in the folder full of wav files you need to convert (after you install sox through your package manager of choice:
#!/bin/bash
out="Mono_88_mu-law"
mkdir $out
for f in *.wav; do
sox $f -t wav -e mu-law -r 8000 -b 8 -c 1 $out/$f
done
If it worked, you’ll end up with a small wav file with a bitrate of 64kbps.
I know probably no one needs this, but it took some time to figure out, so hopefully someone who does stumbles upon it in the future. Also, if anyone would like a proper tutorial on more relevant pro audio stuff, let me know and I’ll start a series.
Here’s an applescript app that will auto-convert dropped files (includes sox).
It drops them into a newly created folder, just like the above bash script.
