[Todd Bradley]

Robert wrote:
I have some overdriven ("clipped") speech audio data which I want to
clean a little.
Is there a simple and maybe free/open-source software for doing this?

I've never heard of such a thing, and from my limited knowledge of
digital audio (18 years in the field) I didn't think such a thing was
even possible! Once you've got digital clipping/distortion, you've
permanently lost information that you can't recover again. Unless
someone's invented software that can go back in time and find the
missing bits, I don't think it's possible to really fix this problem.

Now, if it's just a very small number samples that are maxed out, I
suppose you could massage the samples around them so it sounds a little
better. I did that by hand once to fix little glitches in dialogue
recordings once. But for anything more than a few samples, I don't see
how it's feasible.


Todd.

[Scott Dorsey]

Todd Bradley wrote:

I've never heard of such a thing, and from my limited knowledge of
digital audio (18 years in the field) I didn't think such a thing was
even possible! Once you've got digital clipping/distortion, you've
permanently lost information that you can't recover again. Unless
someone's invented software that can go back in time and find the
missing bits, I don't think it's possible to really fix this problem.

You can't. But what happened was that some folks in the mid-nineties
discovered that the CEDAR and NoNoise impulse noise reduction functions
helped a lot to make clipped material listenable. It can't redraw the
missing part of the waveform, but it makes it less harsh and buzzy.

The current "clip restoration" software is basically a derivation of
the impulse noise reduction systems. It smooths the corners of the
flattopped waveforms.

Now, if it's just a very small number samples that are maxed out, I
suppose you could massage the samples around them so it sounds a little
better. I did that by hand once to fix little glitches in dialogue
recordings once. But for anything more than a few samples, I don't see
how it's feasible.

The "clip restoration" stuff only works for light clipping and it doesn't
fix the problem, it just makes it a bit more listenable. But this can
still be useful for historic archive recordings, for instance, where it
isn't possible to retrack.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Steve King]

"Todd Bradley" wrote in message
...
Robert wrote:
I have some overdriven ("clipped") speech audio data which I want to
clean a little.
Is there a simple and maybe free/open-source software for doing this?

I've never heard of such a thing, and from my limited knowledge of digital
audio (18 years in the field) I didn't think such a thing was even
possible! Once you've got digital clipping/distortion, you've permanently
lost information that you can't recover again. Unless someone's invented
software that can go back in time and find the missing bits, I don't think
it's possible to really fix this problem.

Now, if it's just a very small number samples that are maxed out, I
suppose you could massage the samples around them so it sounds a little
better. I did that by hand once to fix little glitches in dialogue
recordings once. But for anything more than a few samples, I don't see
how it's feasible.


Todd.

Actually, the clip restoration function in Adobe Audition/Cool Edit Pro 2.0
works pretty well. One can specify how much the clipped area is to be
attenuated, then Audition 'rounds off' the formerly truncated peaks. Of
course, if the material is heavily clipped, information will be lost as Todd
says. But, even then, sometimes much of the nastiness can be removed making
otherwise harsh and unpleasant material at least listenable for content as
in speech restoration. Will one be able to recover a vocal track that has
been heavily clipped? Probably not. But, lacking alternatives, it's worth
a try. Demo versions of Adobe Audition can be downloaded. I do not know if
Effects/Noise Reduction/Clip Restoration is enabled in those demos. Check
it out.

Steve King

[Scott Fraser]

The current "clip restoration" software is basically a derivation of
the impulse noise reduction systems. It smooths the corners of the
flattopped waveforms.

This is basically what the "Repair Click" DSP function in Peak does. It
works when there aren't too many consecutive clipped samples. You can
also manually redraw some clips, & if it's brief, render the clip
inaudible. The results are often hit or miss when doing this, & it
seems to work better on ADC clipping than analog clips preceding the
conversion stage.

Scott Fraser

[Daniel Fuchs]

You can't. But what happened was that some folks in the mid-nineties
discovered that the CEDAR and NoNoise impulse noise reduction functions
helped a lot to make clipped material listenable. It can't redraw the
missing part of the waveform, but it makes it less harsh and buzzy.

The declipping feature in Samplitude/Sequoia does exactly that, after
lowering the level accordingly, clipped peaks are reconstructed, and
this works amazingly well.

The current "clip restoration" software is basically a derivation of
the impulse noise reduction systems. It smooths the corners of the
flattopped waveforms.

No, that wouldn't be enough.


The "clip restoration" stuff only works for light clipping and it doesn't
fix the problem, it just makes it a bit more listenable.

With some signals and light/medium clipping, the result can be a signal
with no clipping noise whatsoever, much better than just "listenable".
Choir recordings are an example of a signal that can be restored quite
well (and where even light clipping is very audible).

Daniel