How to clip negative side of a waveform?

Hi, could anyone tell me of a way (or plugin) to clip the negative portion of a waveform?

What I’m trying to do is remove the central channel from a stereo track. I heard it’s not possible but surely it is quite simple, if you just clip the negative from L and R, invert R, mix the two, thus what remains is only what was unique to L. You then repeat this process with the other 3 half-waveforms (L negative, R positive, and R negative).

Use the Nyquist Prompt effect with this command:

(s-max s 0)

If you want to clip at a different position you can change the final value, for example to clip negative peaks below 0.5 linear:

(s-max s -0.5)

That’s what the Vocal Removal effect does Audacity Manual

The thing that is not possible through simple channel manipulation is to “isolate” the centre part.

For removing the centre panned content, all you need to do is to “subtract” the left channel from the right (or right channel from the left). Whatever is left over is what is unique to either the left or right channel - in other words, what remains is the difference between the two channels. The following Nyquist command will do that:

(diff (aref s 0)(aref s 1))

What I’m trying to do is remove the central channel from a stereo track. I heard it’s not possible but surely it is quite simple

You certainly can, but you can’t get a stereo file without the “center”, at least not with simple math. The basic problem is the “left only” and “right only” channels also contain the phantom center channel.

FYI - [u]Clipping[/u] and “negative half”, don’t mean what you thing they mean… :wink: In that Wikipedia image, the top & bottom half of the waveform are clipped (squared-off). The bottom-half is the negative part of the waveform (the part below the center-line).

It’s 39 seconds long. Download that, import it to the timeline and watch the blue waves as you play it.

It may still be true that Avid video editors don’t use waveforms like Audacity does. It uses “baskets of loudness” like SoundCloud (attach).

As a result of that, I had some very strange conversations with Avid editors about how to cure problems like correcting a production with the left and right channels out of phase. Remembering that in the Baskets of Loudness view, there is no phase. One editor claimed they could cure phase cancellation by delaying (time shift tool) one side against the other a little. Piece of cake. Done it a million times.

What made it worse was that it seems to work.

Screen Shot 2014-10-18 at 12.54.01.png

Perfect! It worked, thank you so much Steve :slight_smile:

The Vocal Removal effect is mono, and I wanted to isolate the left, right and center… which I was able to achieve thanks to your help! :slight_smile: It is inexplicably noisy, but it works.

I really think this function should be in Audacity, so I have submitted my feature request here.

I’ve done it! :slight_smile:

Er… that is precisely what I thought “clipping” and “negative” meant!

Thank you for the sample, my method works perfectly on it. You can only hear the left and right “this is my voice” but the center voice vanishes completely… like magic!

Maybe you weren’t talking to me, but I have no idea what Avid video editors are!

I have no idea what Avid video editors are.

That’s my Hollywood Hat. Movies are not cut with razor blades any more. They’re cut on (usually) Avid electronic editors (cousins to Audacity) and the result is conformed to the physical film (if any). The point is, anyone using either Avids or SoundCloud will have no idea what the audio waveform actually looks like because the waveforms are not presented.

Maybe you’re just describing it wrong, but anyone slicing off the negative excursions of performance waveforms just produces highly distorted trash and worse yet, a DC component which may make anything after that crash.

And yes, that’s exactly what LRMono is supposed to do. There is a text narrative associated with that test explaining what each segment is.


But it worked perfectly. The waveform doesn’t remain sliced, it’s just so you can perform operations on the waveform. I have listed the full process here.

The center channel was not missing when I downloaded it! I removed it using my technique (with Steve’s help).

The center channel was not missing when I downloaded it! I removed it using my technique (with Steve’s help).

All four segments are audible unless you’re listening on a mono speaker or sound system. If you do listen that way, then segment four will vanish.

All of the standard Vocal Removal tools or techniques will suck out segment three. Left and right are as identical as possible and that counts as a lead singer which is the point of the tools.


Kozikowski, with the greatest of respect, I feel that you and I are having two different conversations here. From everything you write, it seems like you have misunderstood what the purpose of this thread was to achieve and I get the feeling you are just not listening to me.

I made this thread because I needed help making a technique to remove the central channel, which I successfully achieved with Steve’s help. You then posted a test wave for me to try it on, and so I tried my effect on your test wave, and it worked, successfully removing the central channel and leaving the left and right channels intact.

Unfortunately I think not.
I have replied in the other thread: Stereo Vocal Remover - #3 by steve