Before revision: If SID only occurs for a portion of the signal, it is called "transient" intermodulation distortion.AES Pro Audio Reference for IM Measurement Intermodulation distortion in audio is usually specified as the root mean square (RMS) value of the various sum-and-difference signals as a percentage of the original signal's RMS voltage, although it may be specified in terms of individual component strengths, in decibels, as is common with RF work.
After revision: If SID only occurs for a portion of the signal, it is called "transient" intermodulation distortion.AES Pro Audio Reference for IM Measurement Intermodulation distortion in audio is usually specified as the root mean square (root mean square) value of the various sum-and-difference signals as a percentage of the original signal's RMS voltage, although it may be specified in terms of individual component strengths, in decibels, as is common with radio frequency work.