pitch estimation algorithm explanation? about lpcnet

[drowe67]

This is code written by @jmvalin, but I have been using it for a while.

Yes, [2NB_BANDS] is the pitch period, with a little scaling; [2NB_BANDS+1] is the pitch predictor gain, and can be interpreted as a measure of voicing. [2*NB_BANDS+2] is the LPC model energy, which isn't actually used in the model (it's zeroed out in train_lpcnet.py).

BTW a couple of new pitch estimators are currently being trialled with LPCNet.

[wenyong-h]

Thanks for your explanation.
One more question?
Do you think LPCNet features(18 cepstral coefficients plus 2 pitch parameters) will lose useful information compared to Tactotron features (80-band mel-scale spectrogram features)?

[jmvalin]

18-band cepstrum definitely loses some of the information from a 80-band spectrogram, mostly related to pitch (which is why a good pitch estimator is useful). OTOH, it also does a good job at decoupling the spectral shape from the pitch. That being said, LPCNet should work fine with 80-band Tacotron features if you prefer using that.

[wenyong-h]

Thanks for your great explanations, that's really helpful.

[HaiFengZeng]

@jmvalin Hi, it's a greate Job! I find it hard to understand the pitch extraction process in pitch.c file ,will you give some detail explaination or algorithms about that?Another question is the pitch period range from 32-256,which means the pitch is in [62.5hz,500hz],is that good enough for children speech?