MFCC definition problem?

[dashkil]

i read through many papers related to (MFCC) Mel-frequency cepstrum coefficient: I have confusion about MFCC process:

1) Many says i have do FT (Fourier Transform) on log-spectrum to obtain cepstrum (as mentioned in wiki : definition of power cepstrum)

2) Many says i have do IFT (Inverse Fourier Transform) on log-spectrum to obtain cepstrum.

3) Many refers to DCT-ll (Discrete cosine Transform-2) on Mel-log-spectrum to obtain MFCC.

My question is which one is right: 1) FT or IFT?
2) If IFT is correct than why they are using DCT-ll instead of IDCT-ll; since DCT-ll is similar to DFT or FT.
hence IDFT or IFT should be similar to IDCT-ll.

Need explanation and ur precious opinion. Thanks in advance.

 

[shekofteh]

Typically 3-th point is correct. Notice that the DCT will be applied on the log of energy of filterbanks.