What is Crest Factor?
Crest factor, also known as peak-to-RMS ratio, represents the ratio between the Peak and RMS values in a waveform. In other words, the crest factor gives a relative indication of the peak value within a waveform. A crest factor of 1 signifies a waveform without peaks, such as DC or square waveforms. A higher crest factor means that the waveform has relatively larger peaks. The crest factor is calculated as the Peak divided by the RMS value.
What is PAPR?
On the other hand, Peak-to-Average Power Ratio (PAPR) is calculated by dividing the square of the Peak value (maximum power) by the square of the RMS value (average power). In essence, PAPR is the square of the crest factor. When expressed in decibels, both values carry the same meaning due to the nature of decibel calculations for power and amplitude ratios. The lowest possible crest factor is 1, or 1:1, or 0 dB.
Crest Factor in Audio Engineering
Although the crest factor is usually expressed as the ratio between Peak and RMS, audio engineers sometimes describe it simply as the “difference between the Peak and RMS values.” This simplification is one practical way to understand and evaluate the crest factor.
This difference between the peak and the average energy level of the waveform can indicate the dynamic range of a sound. Generally, in music mixing and mastering stages, a lower crest factor implies a narrower dynamic range and can make the music sound more compressed. Engineers mention the difference between the peak and RMS values to convey information about the waveform’s dynamic range.
However, this is not a mathematically accurate definition of the crest factor, and expressing it as a ratio is a more precise method. Nevertheless, in practical applications, the difference between peak and RMS values is sometimes used to describe the crest factor for ease of understanding and usage.