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Gear / Technical Help => Post-Processing, Computer / Streaming / Internet Devices & Related Activity => Topic started by: rjp on April 25, 2009, 05:26:44 PM
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Last night, I was at a concert featuring a classical duet - quiet stuff, in other words. As my luck would have it, someone right behind me had his hearing aid turned up too high.
It was SQUEEEE! annoying enough to SQUEEEE! listen to the show with this SQUEEEE! happening during the show, SQUEEEE! but listening to the recording was even more SQUEEEE! obnoxious.
Fortunately, the hearing aid noises were pure tones - and a notch filter dealt with them nicely, since they fell outside any notes that the instruments were actually playing.
Here's the basic plan, using Audacity:
- Make sure you have the LADSPA plugin package (http://audacity.sourceforge.net/download/windows) installed. The notch filter doesn't come with Audacity by default.
- Select the area with the hearing aid squeal (or other loud, pure tone that needs to go away). IMO, it's best to spot-fix these instead of trying to filter the whole recording at once, to avoid stepping on anything that shouldn't be eliminated.
- Use Analyze -> Plot Spectrum to figure out the unwanted tone's frequency.
- Use Mag's Notch Filter from the Effects menu. Fill in the frequency, and a band width; you usually need to notch out about 200 Hz, sometimes more. Play with the settings until you get the best result. In extreme cases it may take multiple passes with the filter.
- Find more squeals, and use Ctrl-R to re-run the notch filter with the settings you used. If that doesn't help, undo it, and then enter new parameters into the notch filter.
The result: a recording that doesn't drive me nuts. Sometimes I would get a quiet click where the filter cut in or out, but that's far SQUEEEE! better than SQUEEEE! listening to that damn hearing aid.