That’s The Radio On My Song

Bob Dylan’s oft-quoted complaint that modern recordings “have sound all over them” presumably refers to the overcompression of music as freqently employed by mainstream mastering studios. One myth that has been floating around for somewhat longer is that radio transmission treats highly compressed music more favourably; this is not actually true. But what exactly does the radio do to a song?

To put it bluntly, FM radio transmissions are broadcast with their own compression – that is, on top of whatever compression has been added to the actual recording at the mastering stage. Now, as might seem obvious to the most average passerby with a firm understanding of the physics of sound, compressing a signal that has already been compressed (probably to the practical limits of the medium) is certainly going to result in some loss of sound quality. In most cases, radio compression causes a grungy distortion in overcompressed material.

In fact, as well as compressing the signal, a radio station’s transmission audio processor generally attenuates high frequencies and causes some randomisation of the stereo signal. The stereo distortion may be caused by the presence of a phase rotator in the signal chain; phase rotators are designed to increase the consistency and intelligibility of the human voice by reducing the typically large asymmetry found in voice waveforms.

These are just a couple of the most common ways a song is processed before being broadcast on-air; this is also why many studios release specially-mastered ‘radio mixes’ of singles. For a radio mix, there is no effective ‘loudness advantage’ to be gained from broadcasting a hyper-compressed source track, because the radio compression will make everything the same loudness anyway. However, tracks with less intrinsic compression in the recording will actually sound better on the radio, as they will not be so distorted and more of the original impact of the work will be retained.

Sulhas Sreedhar has created a Flash multimedia presentation which uses some Pink Floyd (and others) to illustrate the development of the loudness war and the effects of overcompression on music.