filtering distortion

[JCauble]

I have a sound file that was over-amplified when originally recorded. I've tried various filters, but still sounds pretty bad. I'm using the free version of Audacity. Does anyone know if the another version of Audacity - or any other kind of software - has the ability to make it usable? I need to remove the distortion. It is a recording of a wedding, so has lots of sentimental value.

Thanks for any tips.

[Trebor]

Audacity does have "clip fix" to reconstruct the flattened peaks and troughs of an over-amplified sound.
http://forum.audacityteam.org/viewtopic ... 377#p17108

BTW it is possible to attach a few (10?) seconds of audio (e.g. WAV or mp3) to a post here if you put it in a ZIP file.
If you posted a bit of your wedding audio people here may be suggest treatments, or tell you if the patient is terminal.

[JCauble]

Wow, thanks for such a quick response! I'll get a snippet and post it when I've got a little more time. But I did take a look and couldn't find a "clip fix" tool. I have Audacity 1.2.6, is that only in another version?

Thanks again, I'll the the clip out as soon as I can.

Jim

[kozikowski]

Audacity 1.2, although officially "Stable," is hopelessly out of date. Audacity 1.3 has all the cool tools and talents. Even though 1.3 is officially "Beta Unstable," it is the basis if the soon to be released 2.0 stable.

Koz

[JCauble]

You guys are great, I really appreciate it.

Here is a snippet with some of the distortion I want to filter out.

Interesting, can't upload MP3 or WMV or WMA. I've included in zip.

[billw58]

Jim:
Here's my diagnosis ...

I can hear the distortion you're talking about, and I think I can see it in the waveform. It's not clipping, so the Clip Fix tool will be no help.

I think the distortion originates in the microphone. Either the microphone was unable to cope with the very low frequencies and created its own internal weird distortion, or the microphone stand was vibrating. The distortion seems to occur during the lowest notes. Rolling off the lowest frequencies is no help.

That sounds like a pretty cheap microphone as well. No high frequencies to speak of. An organ shouldn't sound that muffled. Perhaps it was a microphone placement issue. The file does benefit from some pretty radical high frequency boost (the organ sounds way better) but the hiss comes up to annoying levels.

You might be able to salvage the recording, but you're never going to be able to get rid of that low-frequency distortion. High-frequency boost (+20 dB at 5 kHz shelf), makes it sound better but, as I said, brings up the hiss. You could apply an EQ curve you like to the entire file to get it to sound decent, then try to use Audacity's Noise Removal tool to get rid of the hiss. It's up to you to decide if it's worth all that work.

"You can't make a silk purse out of a sow's ear". Don't believe the things you see them do with audio on CSI - it's all fantasy.

-- Bill

[kozikowski]

I, too, think the microphone wasn't up to the job. Each church has resonance and good organists play to those notes. This can drive sophisticated microphones; condenser, electret, nuts. I hear frequency doubling where the low pedal which should have been. The bass note through the middle of the clip was instead an octave higher and distorted. Anyone else notice the last note at around 9 sec isn't mangled? That's where the performance slid off the resonance of the room and just became normal sound.

I expect a dynamic (moving coil) or ribbon to be the only two microphone types to be able to stand up to that kind of punishment and even with that, some steps would need to be taken to avoid overloading the preamplifier.

You can probably get really good condensers to survive this, too.

Not the microphone on top of the camcorder. That's what this was, right?

Koz

[steve]

A good dynamic microphone would be a good choice, though many of the cheaper ones have poor high frequency response. Ribbon microphones and some condenser microphones are capable of the job but are expensive and delicate.

Most stand-alone microphone pre-amps should be able to cope, but metering can be a problem as often the meters do not respond accurately to very low frequency sound and setting the recording level often requires an element of guesswork. To get a really good recording of a big organ requires very high quality equipment. The dynamic range and frequency range of a big organ is extreme, so it will show up any weaknesses in the equipment. Having said that, good results can be achieved with mid-range equipment provided everything is set up carefully.

The damage in the sample file is not repairable.

[Trebor]

Particular* bass frequencies in the organ music are overly loud and are modulating the sound producing an intermittent vibrato-like effect.

There is a self-ring-modulator plugin from David R. Sky which does the same when its “Lowpass filter” is used …
http://www.shellworld.net/~davidsky/selfring.ny

If someone who knows nyquist could modify Mr Sky’s plugin to include a reciprocal term, so it divides rather than multiplies, then possibly it could then be used to cancel out such bass-induced vibrato-like distortions when used in lowpass mode.

This is a long shot, but is the only thing I can think could possibly correct the distortion in the wedding music.


{* a resonance effect}.

[jtp_60]

As said already, you can't repair this fully ... just try to make it sound better.
I would try some spectral repair tools found on iZotope RX and Adobe Audioion 3.

Juha