Basic noises


Hiss and noise in recordings results from different sources, acoustic and electronic. Amplifiers, radio reception, gramophone records and magnetic tape have different kind of noises. It is usually possible to reduce at least some of the noise in order to make it more comfortable to listen to the music. In principle it would be possible to remove all of the noise, but unfortunately a powerful removal process will also add unwanted alias frequencies into the sound.

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There are sharp clicks especially on shellac and vinyl discs. However, this example is from open reel tape. There are loud clicks in the recording twice a second.


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Usually the hum in a recording is 50 Hz mains hum (60 Hz in the USA). In this particular example the harmonic frequencies extend all the way up to 1000 Hz. This means that there isn't just the 50Hz hum, but there are also components at 100, 150, 250, 350 Hz etc. Some loud low frequency thumps were also removed.


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A recording may get distorted for different reasons. The type of distortion that has been caused by overloading, can often be reduced.

Audience noise in a live concert recording

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This is a brand new recording. Somebody from the audience makes a cough when the orchestra is playing softly. The cough has been removed without touching the original music.