How to process music to a monotone?
March 12, 2010 8:17 PM   Subscribe

How can I remove the component of pitch (or frequency) from an audio waveform, while maintaining the amplitude? I'm looking for a process analogous to desaturating a colour image to black and white: rendering an audio file literally monotonous but maintaining its rhythm (as changes in volume over time).
posted by sixswitch to Media & Arts (24 answers total) 2 users marked this as a favorite
Other than hiring a percussionist that is.
posted by sixswitch at 8:17 PM on March 12, 2010

Here are a few ideas:

1. Spectral editing. There are a few tools that let you edit in the frequency domain, but I haven't found one I'm really happy with.
2. Just use a narrow bandpass filter with a large resonance value. Sweep it up and down until you find a good frequency for the entire duration
3. If you have access to Logic, you can detect the transients in the audio, and then either snap samples or MIDI notes to them. The samples could be a monotone or any sound you want. Same deal with the MIDI notes.
4. You could probably use your audio waveform as input to any number of different sidechaining effects. The typical example is a compressor, but that would turn up the volume when your audio waveform is quiet and turn it down when it is loud - the inverse of what you want.
posted by b1tr0t at 8:24 PM on March 12, 2010

I believe Audacity can do that. For freeware it is very powerful.
posted by JJ86 at 8:24 PM on March 12, 2010

JJ86 — I've had some experience with Audacity so that would be great news. Was there a specific feature you were thinking about? Or were you referring to one of b1tr0t's ideas?
posted by sixswitch at 8:27 PM on March 12, 2010

As I heard your question, what occurred to me would be to convert the sound to an MP3, and then go into the MP3 and change all the frequency components to be the same, without affecting the amplitude components of them all. But that would probably require custom code; I doubt there's a tool that could do that.
posted by Chocolate Pickle at 8:29 PM on March 12, 2010

Can you expand on what you're trying to do? I can't figure out exactly what you're asking.
posted by jjb at 8:31 PM on March 12, 2010

Or nevermind, clearly these other guys know what you're asking.
posted by jjb at 8:31 PM on March 12, 2010

I want to (veeeery roughly) approximate the effect of creating an unpitched arrangement of a piece of music.
posted by sixswitch at 8:37 PM on March 12, 2010

posted by The World Famous at 8:43 PM on March 12, 2010 [1 favorite]

What you want is an envelope filter applied to... something. A single tone maybe, or white noise or pink noise or something. The "envelope" is what the amplitude looks like, without any frequency information. On it's own it's not going to sound like anything at all.

You could probably do this with a vocoder effect - a vocoder is usually used to apply the amplitude bits from something (your voice) to the frequency bits from something else (an instrument). You'll have to figure out what you want your "instrument" to be (like I said, a single sine wave or maybe white noise or something)
posted by RustyBrooks at 8:45 PM on March 12, 2010 [2 favorites]

A ring modulator could also do the trick, if tweaked just right.
posted by The World Famous at 8:47 PM on March 12, 2010

And this is why Audacity drives me nuts! It won't stay open for more than 30 seconds, on Windows or Mac OS. Flargh.

Great ideas, everyone...will try the vocoder first, as soon as I can get Audacity sobered up. If you read this, keep tossing 'em out if you have any others!
posted by sixswitch at 9:35 PM on March 12, 2010

+1 b1trot, you want the opposite of a sidechain compressor.

One supposes you could sidechain the sidechained track.


Track 1 - original source
Track 2 - sidechain of original source compressing white noise
Track 3 - sidechain of track 2 compressing white noise

So you're inverting the signal twice. You'd have to mess with the compression levels to get something has the effect you want, but this should get you in the ballpark.
posted by MesoFilter at 9:38 PM on March 12, 2010

Do you have a mac and logic? Logic has a plug in oscillator/filter effect which can do this very easily.

The compressor sidechain idea is a decent one, though. But I would do it with a gate/sidechain. The Pgm material with rhythmically open a gate which white noise etc is running through. I think the logic oscillator thing would track much better though. Gates/comps would probably not be high resolution enough, so to speak to render much more than the basic rhythmic feel of the source material.

The line 6 m9/m13 has a freq shift effect which can do this as well.
posted by tremspeed at 10:30 PM on March 12, 2010

tremspeed and MesoFilter: I have just gone through Audacity (crashes on Win & Mac), Kristal Audio (no routing), and Reaper (can't route to the sidechain plugin). I don't have Logic, but I have access to a Mac & PC. Do you guys know of any free sequencers / VST hosts that might be up to this? Or am I missing something on one of the previous (free and therefore sketchy) programs?
posted by sixswitch at 11:04 PM on March 12, 2010

Sorry, haven't used those.

Bias Peak has something like a frequency shifter effect, try getting a demo version?
posted by tremspeed at 11:24 PM on March 12, 2010

Seconding Melodyne.
posted by Blazecock Pileon at 11:29 PM on March 12, 2010

Audacity is a great piece of software and not at all sketchy. Logic 9.1 crashes far more for me than even Audacity 1.3 Beta.

You might try the Ableton Live free trial - I think it works for 30 days for free. Live has a lot of effects, including a nice sidechaining compressor.

I just poked around in Audacity 1.3. There are tools for finding beats, silence, and sound, but they generate an annotation track. I'm not sure how or even if you can turn that in to sections of generated tone. I generally use Audacity for basic sound editing - sometimes it is easier and more powerful than Apple's Soundtrack (or I need to spend more time with the Soundtrack manual).
posted by b1tr0t at 11:40 PM on March 12, 2010

Sorry, didn't mean to dis Audacity -- I just keep having bad luck with it. I appreciate the help. I think I will try the Ableton trial...but maybe tomorrow morning!
posted by sixswitch at 11:42 PM on March 12, 2010

If you only want the rhytmical aspect (no tones), use white noise as target for a vocoder, controlled by your source audio. You will end up with no tonal information, only the rhythm, like a ghost. Number of bands controls detail. There is a vocoder in Ableton Live.

You can probably also do this with other means, but this is very simple to do with a vocoder, it is what they do.

If you still want a "monotone" (and a representative monotone from the source), I think you have to use Melodyne Editor, polyphonic mode, detect the most prominent frequency, and either delete all the others or adjust them all to the same. Or you could find the prominent frequency by ear or some other editor, and reinsert this tonal frequency as a single tone in the above mentioned vocoder.
posted by gmm at 12:19 AM on March 13, 2010

Wow, thanks everybody. Got a rough version hacked together using the built-in sidechain compressor in the trial for Ableton. I learned a crapload tonight!
posted by sixswitch at 12:44 AM on March 13, 2010

I think Praat could probably do this well, though I'm not sure of the exact procedures you'd use.
posted by greatgefilte at 10:35 AM on March 13, 2010

I'm not sure how to solve this problem in Praat either, but there are some cool tools over at the Princeton Sound Lab. Among the cool things there, Tapestrea is a powerful tool for spectral manipulation. I'm not sure it will solve sixswitch's problem, but others that visit this thread might find it interesting.
posted by b1tr0t at 11:13 AM on March 13, 2010

Wow. Praat and the stuff at PSL just blew my mind. Killer links, everybody, and thanks for getting me up to speed so fast and sharing your knowledge of what for me is unfamiliar territory.
posted by sixswitch at 11:42 AM on March 13, 2010

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