[LAU] How is the bass mixed? Per-channel frequency analysis? Histogram?

[Matt Garman]

Hi Dan,

Thank you for taking the time to put that together!  Looks like I have
a fair amount of learning to do before I can make sense of exactly
what's going on (I mean, I get the gist at a very high level, but
don't understand the details enough to hack the code).

I ran it on a few tracks that I thought would be interesting.  Clearly
this list has a number of folks with mixing experience and/or
knowledge, maybe they can comment on what I'm seeing:

1. Leo Kottke "The Driving of the Year Nail" - first track from 6- and
12-String Guitar.  Looks like there's a definite bias towards the left
channel.
    http://raw-sewage.net/images/stereoscope/kottke.png
I would have expected both channels to be perfectly equal, since this
is exactly one instrument.  (I have no mixing or studio experience,
keep in mind, just a guy who likes music.  So this is what my
uninformed intuition says.)

2. The Beatles "While My Guitar Gently Weeps" - from The While Album.
    http://raw-sewage.net/images/stereoscope/beatles.png
I picked this since there was a mention of Beatles albums having the
bass mixed only to one side.  If I could hack the code to do a low
pass filter, this might be an interesting track.  But, it appears to
me there's a definite bias for the lowest frequencies to be panned to
the right side.

3. Above & Beyond "Let Go" - from Anjunabeats Vol 8.
    http://raw-sewage.net/images/stereoscope/above_beyond.png
Just curious what some electronic music looked like... This could well
be a mono mix?

4. Beethoven "Moonlight Sonata" - from a collection of Beethoven's
piano sonatas (not sure who the performer is or label, too lazy to go
pull the CD)
    http://raw-sewage.net/images/stereoscope/beethoven.png
This graph looks kind of weird.  Is there really that little
high-frequency information?

Anyway, thanks again Dan!  I'll keep playing with the tool and trying
to learn to see if I can come up with any more interesting info.

-Matt



On Fri, Feb 7, 2014 at 3:43 PM, Dan S <danstowell+lxau at gmail.com> wrote:
> Hi Matt,
>
> Here's a Python script which analyses a set of files in a specified
> folder. They have to be file formats understood by libsndfile - which
> allows for flac/wav/aiff and some others, but not mp3. It takes maybe
> 5 to 10 seconds per track, but eventually it produces a plot as a PNG
> file.
>
> https://gist.github.com/danstowell/8872466
>
> (Also blogged: <http://mcld.co.uk/blog/blog.php?417>)
>
> Best
> Dan
>
> 2014-02-05 Matt Garman <matthew.garman at gmail.com>:
>>
>> I have a collection of FLAC files, all ripped from my CD collection
>> What I would like to do is run an analysis across all the music to
>> determine how the bass/lower frequencies are generally mixed.  For
>> example, how much content below (for example) 150 Hz is on the left
>> channel versus the right channel?
>>
>> 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
>> ...
>>
>> Then I can look at the two channels of a song, and if the histograms
>> are approximately the same, I can assume the bass was mixed equally
>> to both channels.
>>
>> 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.
>>
>> Note that I don't need any kind of graphical output, as this needs
>> to be wrapped up in some kind of batch processing script---I have
>> about 11,000 files to analyze!
>>
>> 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 the overwhelming majority of my music has
>> the bass mixed equally, sending only one channel isn't a problem.
>> But if I choose the "L" channel to send to the sub, and much music
>> has the bass mixed only to the "R" channel, then I won't be able to
>> hear the low frequencies.  I want to find out how often this might
>> happen.
>>
>> Thanks,
>> Matt
>>
>>
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>
>
>
> --
> http://www.mcld.co.uk