6 Feb
2014
6 Feb
'14
12:07 p.m.
On 02/05/2014 04:36 PM, Matt Garman wrote:
I'm not sure if "histogram" is the right
word, but in my mind what
I'd like to see, per-channel, is something like this:
150--125 Hz: x samples 125--100 Hz: y samples 100--80 Hz: z
samples ...
a low-pass or band-pass filter, followed by an RMS meter can do what
you want. Though ideally you'll look at the stereo-phase correlation
(after filtering).
[..]
I am a programmer, and thought it would be easy to
quickly hack
something up that would do this, but I have no experience with
signal processing, and as I started reading about this, I quickly
got in over my head! So I was hoping there might already exist a
tool that has this functionality.
There are various GUI tools and Plugins for audio-analysis. But that's
no fun for batch-analysis of > 10K audio-files.
I don't think a commandline tool exists. You might be able to hack
something together jalv.console (http://dev.drobilla.net/ticket/943)
or vamp-simple-host or maybe ecasound. But it'll probably be easier
to whip something up from scratch; some simplified pseudo-code:
foreach audio-sample as inL, inR {
/* 1st order low pass filter */
left += w * (inL - left);
right += w * (inR - right);
/* calc RMS */
rmsL = left * left;
rmsR = right * right;
if (rmsL > threshold_squared) ++L_above;
if (rmsR > threshold_squared) ++R_above;
}
w ~ omega, is the filter constant. For -3dB at freq:
w = 1.0 - e^(-2.0 * π * freq / SampleRate);
see also https://en.wikipedia.org/wiki/Low-pass_filter
This should get you started at least, there's plenty of example code
and literature around for more advanced filters.
The motivation for this is: I have a hardware DAC
(digital audio
converter) in one part of my house, and a subwoofer in another.
There is a single coax run between the DAC and subwoofer, so I can
only send one channel.
If you only have one subwoofer, just downmix to mono before sending
the audio there.
Cheers!
robin