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Quiet Thoughts on a Deafening Problem - May 2014
AES Journal Forum
Why Are Commercials so Loud? ' Perception and Modeling of the Loudness of Amplitude-Compressed Speech*
The level of broadcast sound is usually limited to prevent overmodulation of the transmitted signal. To increase the loudness of broadcast sounds, especially commercials, fastacting amplitude compression is often applied. This allows the root-mean-square (rms) level of the sounds to be increased without exceeding the maximum permissible peak level. In addition, even for a fixed rms level, compression may have an effect on loudness. To assess whether this was the case, we obtained loudness matches between uncompressed speech (short phrases) and speech that was subjected to varying degrees of four-band compression. All rms levels were calculated off line. We found that the compressed speech had a lower rms level than the uncompressed speech (by up to 3 dB) at the point of equal loudness, which implies that, at equal rms level, compressed speech sounds louder than uncompressed speech. The effect increased as the rms level was increased from 50 to 65 to 80 dB SPL. For the largest amount of compression used here, the compression would allow about a 58% increase in loudness for a fixed peak level (equivalent to a change in level of about 6 dB). With a slight modification, the model of loudness described by Glasberg and Moore  was able to account accurately for the results.
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