Infinite loop in "Change gender"

[YannickJadoul]

I got an issue reported at YannickJadoul/Parselmouth#68 by @auspicious3000, that in some cases, "Change gender"'s execution blocks.

@auspicious3000 very kindly provided me an minimal reproducing example of a case in which this happens, and it seems that the error lies somewhere in Praat, as I can reproduce the issue in Praat.

The following should reproduce the error (tried out in Praat 6.1.51, and in the latest master version):

• Read the FLAC file in this zip file into Praat: 2552-132097-0069.zip
  (Apologies for the zip file, but GitHub only allows to upload certain file types/extensions into an issue.)
• Run "Change gender", with parameters: 50, 250, 0.79, 105.469, 1.487, 1.0
• Praat hangs and gets into an infinite loop.

I've compiled a debug version of Praat and found out the following:

• According to my debugger, the infinite loop happens at

  praat/fon/Manipulation.cpp

  Line 418 in 586bc8b

  while (ttarget < endOfTargetVoice) {

  as endOfTargetNoise is +inf.
• endOfTargetNoise is +inf, because of a division by zero at

  praat/fon/Manipulation.cpp

  Line 399 in 586bc8b

  finishingPeriod = 1.0 / RealTier_getValueAtTime (pitch, endOfSourceVoice);

I haven't looked further than this, trying to figure out why RealTier_getValueAtTime (pitch, endOfSourceVoice) on line 399 results in 0. If I do figure out more, I will update!

[PaulBoersma]

For this example, Praat 6.2.02 will bail out with an appropriate error message, which is "Change gender: your pitch manipulation would lead to negative pitch values." Thanks for the excellent bug hunt.

[YannickJadoul]

Thank you for solving this!

One small additional question: in older versions of Praat (before the 6.2.02 fix), is there a way of detecting when this would happen, in order to not call "Change gender" on this audio with these parameters, and avoid getting stuck in this infinite loop?

[PaulBoersma]

Instead of "Sound: Change gender", you could compute the pitch yourself (with the given minimum and maximum pitch) and do "Sound & Pitch: Change Gender". Once you have the Pitch, you can query its minimum (without interpolation) and median, and check whether the resulting pitch value will be less than 0:

scaledMinimum = minimum * newMedian / median
resultingMinimum = newMedian + (scaledMinimum - newMedian) * pitchRangefactor
if (resultingMinimum <= 0.0) ...

[YannickJadoul]

Thank you very much! This will be quite useful to @auspicious3000.