Propeller Head Plaza

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RE: Phase Distortion, dv/dt, and Slew Rate

Posted by Tony Lauck on December 21, 2015 at 19:06:35:
The longer you sample, the greater the chance of a random collection of waves adding up and creating a large peak. Most recordings that are made cleanly (uncompressed and not subject to tape compression from loud recordings) will have a crest factor around 18 dB. With mild compression the crest factor will be around 15 dB. Percussive recordings can have much greater crest ratios, of course. Also, the recording style affects crest ratios, due to reverberations, etc.

These figures relate to short term period of averaging (0.5 to 2 seconds) during which the music is homogeneous. If you average over longer periods there will be occasional larger peaks and the possibility depends on the number of individual waveform sources. If musical dynamics come into play, then the crest factors can easily get to 25 dB or more.

If there is a rare peak over the ability of the recording or playback this may or may not be audible, depending on the technology. For example, momentary clipping of a stable amplifier on a percussive transient will not be audible if this happens infrequently in the course of a track. However, if the amplifier is unstable (i.e. incompetently designed) then a temporary overload on one peak may cause the amplifier to misbehave for an extended period. Similar problems happen with clipping in digital recording or playback. With LP playback peaks can cause needles to jump out of the groove, etc...

These are all factors well familiar to recording engineers, especially mastering engineers.