I’ve been playing around with noise reduction features of different software programs, to remove hiss, fans, air conditioners and wind noise. Here’s a very impressionistic report on the programs I tried.
I should mention first off that I won’t be doing any acoustic analysis on the doctored files, at least at this stage. I was doing this in order to make transcription easier. Most of the tapes probably aren’t clean enough to do most types of analysis, even if the noise removal didn’t remove other vital information.
I’ve tried four pieces of software:
- Praat (free from praat.org)
- CoolEdit 2000 (registered in 2002; no longer available)
- SoundForge 8.0 with noise reduction plug-in ($125 or so, academic license)
- Audacity (free from audacity.sourceforge.net)
Nothing was a magic fix, of course. There’s no substitute for making good quality recordings in the first place. But hindsight is wonderful, and it’s often not possible to record in idea circumstances.
The recordings are all digitizations of analogue (cassette) tapes made at 44.1kHz or 48KHz between 2004 and 2006. The 2004 ones were made in Audacity and the 2006 ones were done with SoundForge (but this didn’t seem to make a difference).
My Praat method was brute force – identify the frequency band where most of the background noise occurs and fading that area of the spectrum by 24dB. It works, sort of. But it’s not very good.
SoundForge has noise reduction and anti-clip algorithms, but I found that they performed very badly on my recordings. They either made no difference or introduced more distortion than they removed.
Audacity and CoolEdit both have a multistage process where a profile of the noise is analysed and those frequencies are dimmed. CoolEdit’s clipping reduction feature produced clearer audio than Audacity’s, but it also introduces tones at random points in the recording – it’s a test feature and you have to pay extra for a version which doesn’t introduce random tones. CoolEdit is no longer supported, though, and its replacement (now maintained by Adobe) is quite expensive. Cooledit’s noise reduction is about equal to Audacity’s. On the settings I used, CoolEdit seemed to produce a little less distortion in the signal.
Here are some comparison clips.
- input file.
- Audacity – noise reduction
- SoundForge – audio restoration
- CoolEdit – noise reduction (no clips in this sample)
- (No Praat sample – there was no consistent noise at a specific frequency in the sample)
The recording was made in the 1960s and I digitised a cassette copy – I don’t have any more information than that.
(I’ve been meaning to do this for some time, but Tom’s post reminded me. I used the same method that they recommend, although I didn’t spend much time playing with different settings to get an optimal output.)
PS: bonus points for identifying the language.