Multitone Audio Test Signal

Generate multitone audio test signal

A Multitone signal can be used to test an audio system. The references provide a review and extensive bibliograohy on this topic. Newer references are also available in the Audio Engineering Journal by searching on the keywork multitone.

The strategy for this signal is that it is to have many sinusiodal signals interspersed with many FFT bins of zero signal. The signal channels provide a masure of the freqwunecy response of the test system, and the empty channels allow an estimate of the distortion plus noise generated within th esystem. This function incldues a spoecified number of frequencies per octave of bandwidth in those octaves with enough FFT bins to provide an empty channel between signal chanels. For the lower octaves, the band is filled alternately with a sinusoid and an empty channel.

This code produces a multitone signal with a specified sample rate and number of samples. One challenge in generating a multitone signal is choosing the phases of the multiple tones to reduce the crest factor (ratio of peak to rms level). This code takes a very simple approach of using random phases for the individual tones. Random phases usually provide moderate crest factor, but are not guaranteed to do so. The challenge is resolved by generating several signals with random phase, and selecting the one with the lowest crest factor.

The upper limit of the for loop in line 41 can be set to a convenient value to obtain a reasonable crest factor. The default value of 10 generally gives crest factor less than 3.9, occasionally lower. Choosing a higher value can provide a crest factor a bit under 3.5.

References

Eugene Czerwinski, Alexander Voishvillo, Sergei Alexandrov and Alexander Terekhov, Multitone Testing of Sound System Components'Some Results and Conclusions, Part 1: History and Theory, JAES (49)11, Nov. 2001

Eugene Czerwinski, Alexander Voishvillo, Sergei Alexandrov and Alexander Terekhov, Multitone Testing of Sound System Components'Some Results and Conclusions: Part 2: Modeling and Application, JAES (49)12, Dec. 2001