Crackle on Tape Recording

[Dan McDonald]

I've been trying the blind de-convolution ideas using the spectrum analyzer and the paragraphic equalizer on a number of different tapes recorded under different conditions.

For some reason, one fairly common result appears to be a kind of "crackling" sound in the vocals as the wave form gets close to being uniform. This is most evident with cassette tapes made from the audience.

I've found using the median filter or the average filter seems to help somewhat, but sometimes that introduces artifacts into the music. Also, De-essing using the dynamics processor sometimes helps. I'm not certain as to what is causing the problem. Any ideas?

Dan McDonald

[This message has been edited by Dan McDonald (edited 02-01-2002).]

[Craig Maier]

Re: \"crackling\" vocals

Is it possible that you are overloading the paragraphic EQ? That would make a crackling sort of sound. Try decreasing its output gain after you make the response correction and see if it goes away. Also, keep an eye on its overload light which is an indication of clipping distortion.

[Craig Maier]

Re: \"crackling\" vocals

Are you using any other filters other than the paragraphic eq? In other words, are you using it in the Multifilter context with a bunch of filters? If so, maybe one of the other filters are becomming overloaded and you just did not notice it. Just another guess.

[Dan McDonald]

Re: \"crackling\" vocals

Hi Craig -

I don't think I'm overloading, as I keep the output pretty low and haven't seen any red lights flashing, but I'll keep working to see. Thanks for the suggestions.

Dan McDonald

[Dan McDonald]

Re: \"crackling\" vocals

Thanks, Craig. No, I haven't been using the multifilter when this happens. I'll work some more on it this week to see if I can figure out the problem.

Dan

[Dan McDonald]

Re: \"crackling\" vocals

Craig, this is most noticeable with music tapes recorded from the audience (with a cassette recorder circa 1973). Typically, the recording is a little muddy sounding to begin with. Could this just be the quality of the recording itself, which you typically don't hear because it's masked by the overall muddy sound, but, when you re-work via the paragraphic equalizer, the poor quality of the recording becomes clearer?

just a guess. I don't seem to be anywhere near overloading. What I notice is that the pkf file looks very compressed before I work on it, then has a lot more clearly defined highs and lows after the equalization.

Dan

[Craig Maier]

Re: \"crackling\" vocals

That is an interesting theory. I suppose that it makes some sense. The original recording may have had some overmodulation distortion on the tape because of a saturated amplifier or tape head. Maybe you are now hearing that distortion because you have extended the frequency response of the recording. In other words, you are now hearing more of the harmonics of the source of overloading. Certainly possible.