Thanks Audacity.

Downloaded a track from a compact cassette that had been recorded of a rock band in 1970, using a Sony mono portable recorder and mike, with a view to cleaning it up a bit. Using the equaliser and experimenting with some drastic settings it was found that there was a buzzing droning noise in the 100 to 180 Hz range that was masked when listening to the original record in but obviously was detracting from it. With that Hz range greatly reduced and a few other minor equaliser tweaks the recording has turned out remarkedly good considering it’s humble origins. It is much more clean and crisp than before.

So thanks very much to those who have made Audacity what it is, a very useful tool :slight_smile:

If that buzzing noise was mains hum there may be additional hum-noise peaks (harmonics) at 240Hz, 300Hz, 360Hz , etc, you can remove those with a notch filter …

Mains hum? Is that generated by mains power used to run the recorder? This one was probably battery powered, if mains than 240volt.

“Mains Hum” is everywhere. It is caused by AC mains electricity power and radiates through the air. Audio cables have “shielding” to reduce the interference from this noise and will usually succeed in reducing it to a negligible level but it is difficult to totally eliminate it. Mains hum can be picked up by inadequately shielded equipment, by proximity to higher than normal interference (for example if you live near an overhead power-line), and for mains operated recording equipment it can be picked up from the mains power itself if the power supply is inadequately smoothed or the equipment is inadequately earthed. Here is the Wikipedia article:

Even if the tape player is currently battery powered, there could be mains hum recorded on the tape from when the recording was made.

The voltage of the mains electricity doesn’t make a difference to the mains hum, it’s the frequency, either 50Hz (in Europe) or 60Hz (North America) , any mains hum will occur at that frequency and multiples thereof (aka harmonics).

If you do a frequency analysis on a region of the recording which should be silent (see Audacity “analyze” menu, “plot spectrum”) you may see the regular spike pattern of mains hum …

That’s probably it then, 1970 technology, amplified guitars etc nearby, lighting and so on. Made a noticeable difference.