CDP Sound Examples – STRETCHING

Time and Spectrum Stretching

SOURCE SOUND

Single marimba stroke
(converted to an analysis file)

TRANSFORMATION

Time-stretched
Spectrum-stretched

DESCRIPTION
~ CDP Functions: TIME STRETCH / SPECTRUM STRETCH ~

• Having 'analysed' this to create a frequency amplitude analysis data file, we then STRETCH it in TIME, using exstr1vs.brk, a time-varying breakpoint file. This is designed to stretch the beginning of the sound quite a bit (8 times) – normally one would do this in several stages in order to improve the quality of the result.
• What sounds like a solid single stroke in the original starts to break up when stretched to this degree, showing that there are in fact multiple impacts.
• We now take this result and STRETCH the SPECTRUM by a factor of 5, starting at a very low frequency and working upwards in order to affect the whole of the sound.
• We easily hear the change in timbre caused by the stretch. Note that the spectrum stretch does not affect the length of the sound.
• A completely different aural result would occur if the spectrum were to be compressed (value < 1) below a high frequency split point.

Additional Information

PARAMETER SETTINGS: Time (L) Spectrum (R)
(Click on image to view fullsize)

KEY POINTS

spectrum stretch parameters

• Mode 1: stretch above frequency split
• frequency split = 20 (starts low: 20 Hz)
• maximum stretch = 5 (transposition ratio)
• exponent = 1 (linear stretch 'curve')
• depth = 1 (full stretch effect)

SUPPLEMENTARY FILES USED

[exstr1vs.brk]
Time Stretch-factor
0.00 8   
0.20 8   
0.21 4  
0.50 5 
1.00 2