Audacity Forum

Hi, I'm new here. Am a 50's some audio amateur, need some help.

I recorded a lovely chorus+piano concert this weekend on my Oly DM-520. Having previously used mp3 and auto, this time I wanted better quality - so used PCM settings, manual audio, internal mike, did a sound check, etc. .
But after listening to first half concert I determined some loud passages were distorted (apparently over-high gain on the signal). Switched to auto, and seemed better (but one can hear the AGC, alas).

Back home in Audacity I used "find clip" of 1.3x beta - Audacity shows no clipping - but the waveform is clearly flattened at the top/bottom.
I used A's plug-in Clipfix and it seemed to make no difference.

I've read messages here, and elswhere - and this type of distortion is tought to deal with, I gather.

Is there any way to

• a) recover some of the natural waveform (clipped volume) ... and
  b) remove the staticky sound of the distortion?

WH

An expander will make peaks more peaky : it increases the gain above a threshold, [It won't make a peak out of a plateau though].
But I wouldn't get your hopes up of being able to cure this type of distortion.

An expander performs the opposite function [to a compressor], increasing the dynamic range of the audio signal.

http://en.wikipedia.org/wiki/Audio_leve ... ion#Basics

You can attach afew seconds of mp3 of a distorted bit to your next post, [file size less than 1Mb].

woodhands wrote:this type of distortion is tought to deal with, I gather.

Yes it is.

If it is only very slight, then the clipfix.ny plug-in can be very effective (should only be used on short sections to "recover" the occasional clipped peak). By the time the distortion is really noticeable it becomes a salvage job rather than restoration.

Clipfix is included in Audacity 1.3.12

woodhands wrote: I recorded a lovely chorus+piano concert this weekend on my Oly DM-520. ...
But after listening to first half concert I determined some loud passages were distorted (apparently over-high gain on the signal). Switched to auto, and seemed better (but one can hear the AGC, alas)......Is there any way to

• a) recover some of the natural waveform (clipped volume) ... and b) remove the staticky sound of the distortion?

WH

in general not really.
if you clipped then you lost the *information* needed to change anything.
if you didnt clip for more than a couple of milliseconds maybe you can fix it good enough.

don't know about oly but zoom H series have input gain settings high low and mid , plus a knob to tweak volume. Most audio recorders opposed to voice oriented ones will also have such features.

always try to record -18 to -24 dB lower than your expected max.
you can always amplify it later to max the volume.

if you have a really wild dynamic range then you may have to also use some compression option which is a smaller evil than clipping.

whomper wrote:always try to record -18 to -24 dB lower than your expected max.

The "ideal" amount of headroom depends on several factors. You only ever need >0dB headroom - the important thing is that clipping distortion is avoided.

The more headroom that is given, the less dynamic range is available.
Allowing for lsb inaccuracy and overhead from filters, 16 bit provides < 90dB dynamic range. If you intend to allow 24dB headroom, but estimate the level a few dB on the conservative side, you could easily be restricting the dynamic range to less than 60dB, which is lower than can be achieved with a good cassette recorder.

Greater degrees of headroom can be allowed when using equipment at greater bit depths without significant detrimental effects, but at 16 bit there is still the need to aim for a "substantial" recording level. In part the "ideal" amount of headroom to allow will depend on your confidence in how accurately you can estimate what the maximum peak level will be. In this sense "headroom" is essentially allowing room for error.

An expander performs the opposite function [to a compressor], increasing the dynamic range of the audio signal.
You can attach afew seconds of mp3 of a distorted bit to your next post, [file size less than 1Mb].

Thanks to all for your advice - especially to keep some headroom. (If 24db is too much to retain full dynamic range, maybe 10-15? my device doesn't have numbers/marks to indicate, so I imagine the moving bars s/be about 10-15% below the peak)

Attached is brief sample from two voices ... listen carefully to hear the crackly top.

If an expander merely expands (say) the clipped parts by, somehow, sensing what would have been higher amplitude, that won't help. What I most want to do is remove the distortion sound effect - the crackly or staticky sound that comes from overmodulating the signal. Is there a noise remover that works on say 10-15 sec sections to pull out only that sound?

WH

Woodhands you've attached an Audacity (.aup) file which doesn't contain any audio.

To attach audio to a post it needs to be in mp3 or wav (or another audio format put in a zip file), not bigger than 1Mb, (typically that's only about 10 seconds).

woodhands wrote:If an expander merely expands (say) the clipped parts by, somehow, sensing what would have been higher amplitude, that won't help. What I most want to do is remove the distortion sound effect - the crackly or staticky sound that comes from overmodulating the signal. Is there a noise remover that works on say 10-15 sec sections to pull out only that sound?

If the peaks are clipped flat, (rather than just a bit squashed), then yes an expander is no use " it can't convert a plateau into a peak".
If they are clipped absolutely flat then clipfix is your only hope: it estimates what the clipped peak should have looked like by interpolation.

NB: you may have to reduce the amplitude of the waveform before applying clipfix to give headroom for the clipped peaks to be drawn in by clipfix.

If the peaks are clipped flat, (rather than just a bit squashed), then yes an expander is no use " it can't convert a plateau into a peak".
If they are clipped absolutely flat then clipfix is your only hope: it estimates what the clipped peak should have looked like by interpolation.

Understood.

NB: you may have to reduce the amplitude of the waveform before applying clipfix to give headroom for the clipped peaks to be drawn in by clipfix.

Yes, I did that. And clipfix in 1.3x beta didn't seem to do anything.

Trebor wrote:Woodhands you've attached an Audacity (.aup) file which doesn't contain any audio.
To attach audio to a post it needs to be in mp3 or wav (or another audio format put in a zip file), not bigger than 1Mb, (typically that's only about 10 seconds).

Hmmm ... I thought the Audacity file included the data in a new format; is it just a file with data for manipulation but with no sound in it? How does that work?

Sorry .... here is the mp3 clip of two different voices, recorded sections.

WH

woodhands wrote:is it just a file with data for manipulation but with no sound in it? How does that work?

See here: http://wiki.audacityteam.org/wiki/File_Management_Tips
This is pretty crucial so if in doubt, ask.

Yep that’s overload distortion.

Not a lot that can be done. I’ve butchered the spectrum, (have a look at the before and after frequency analyses to see what frequencies I’ve amputated),
and applied “Floorfish” (free) expander at different frequencies …
I slso tried "centre pan isolation" using Kn0ck0ut, it has less overload distortion but sounds computery, (digital artifacts), basically swapping one type of distortion for another ...