2021.01.02 12:12
how to adjust the playback speed of a tape recording quickly
I often encounter the issue of having an audio recording transferred from a reel-to-reel tape to my computer with incorrect speed: either the tape recorder used for the original recording was spinning too fast or too slow, or the tape recorder I used for the transfer was spinning incorrectly. This creates a problem because the sound is noticeably off-pitch, but it's hard to guess exactly how much to slow it down to get it just right. Recently, I came up with a neat trick. In recordings made on a tape recorder, you often hear a 50 Hz hum in the background from the power grid. So all you need to do is look at the sound spectrogram, see if there's a clear peak around 50 Hz, check how far it is from 50 Hz, and slow down the sound so that this peak aligns perfectly with 50 Hz. Tested and it works like a charm.
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