Mel Cepstral Distortion I am working on a speech synthesis model and I am looking to evaluate my synthesized speech. I found that most people use the Mel Cepstral Distortion (MCD) which can be calculated by the formula:

$$\frac{10\sqrt{2}}{\ln10}\frac{1}{T}\sum_t\sqrt{\sum^{25}_i 2||mc(t,i)-mc_{synth}(t,i)||^2}$$

I have ground-truth speech and the synthesised version so I calculate the MFCCs for both (taking 25 coefficients) and then apply the formula. The result I get is around 300, which seems orders of magnitude larger than what I should get. I tried doing cepstral mean normalization which brings the number down to around 30 but I notice that most of the time this number is &lt;10. The speech I synthesize is not so bad so I must be doing something wrong. Does anyone have any ideas?

P.S. The way I produce the speech ensures that it be aligned with the original(more or less). I wonder if a slight misalignment could cause this issue and if so should I use DTW to align the audios?

Edit
Also If anyone knows of a library that calculated MCD when given an audio file then I could use that to compare my results.
Ok so here is what I found. The distance is dependent on the way that the mfccs are calculated. This makes sense to me and also explains why cepstral mean normalization affects the values of the MCD. 

I found this implementation (https://github.com/MattShannon/mcd), which unfortunately did not support .wav files. I ran this and it gives results that are in the correct range for its test examples. I looked into the code and found that the the difference was not so much in the calculation of the MCD (which is straight forward) but rather the mfccs. The library I was using gave mfccs at a different scale (I tried python_speech_features and pyspeech). Using the mfccs from Matlab gave me mfccs in a similar range to that of the repo so I opted to use those. 

A noteworthy point is that the first coefficient is quite large which is why it is ignored in (https://github.com/MattShannon/mcd) so I did the same. There are some artifacts in the speech I synthesise which likely accounts for why my MCD is still above 10 but its still lower than 30 now.