posted 4 years ago

Greetings to all!)

Recently became interested in analyzing audio files.

My task this - read the source file and make him FFT...

Here such I turned the code:

I do not know if he is right, but he will come out about the following values: (here are a few for example)

In general please help fix bugs in it (if any)

Thanks in advance!)

Recently became interested in analyzing audio files.

My task this - read the source file and make him FFT...

Here such I turned the code:

I do not know if he is right, but he will come out about the following values: (here are a few for example)

In general please help fix bugs in it (if any)

Thanks in advance!)

posted 4 years ago

Lengrand,

1. I've moved your post, because it's

2. I have no idea how the FFT algorithm works, but you should be aware that Java

Winston

LenGrand Bibi wrote:I do not know if he is right, but he will come out about the following values: (here are a few for example)

Lengrand,

1. I've moved your post, because it's

*definitely*not for beginners.

2. I have no idea how the FFT algorithm works, but you should be aware that Java

`int`'s are

*signed*, so the bit reversal stuff you have going on might produce anomalous results.

Winston

"Leadership is nature's way of removing morons from the productive flow" - Dogbert

Articles by Winston can be found here

posted 4 years ago

Since we don't have access to your audio file we cannot possibly know whether or not the values you have printed are correct!

Your FFT method just swallows the results! The FFT can be done in place so there is no need to create copies of the data. Just change to

and remove the code to copy the values for the input arrays to the xReal and xImag arrays. By doing this the FFT results will be available in the input arrays.

A quick simple test of your FFT methd using

indicates that the FFT is probably implemented correctly but one needs to do much more extensive testing to be certain. The 'bit twiddling' is correct.

The decode() method will only work for one format of audio files (little endian signed) so you will need to deal with other encoding.

One major problem you seem to have is in understanding what the results of the FFT mean. For that you need to spend some time learning about spectral estimation which means you will need a thorough understanding of Fourier transforms and in particular the Discrete Fourier Transform. I have a strong background in this and I can help but forums are very poor for '1 on 1' teaching of complex topics so you will need to spend a lot of time reading books and articles.

Your FFT method just swallows the results! The FFT can be done in place so there is no need to create copies of the data. Just change to

and remove the code to copy the values for the input arrays to the xReal and xImag arrays. By doing this the FFT results will be available in the input arrays.

A quick simple test of your FFT methd using

indicates that the FFT is probably implemented correctly but one needs to do much more extensive testing to be certain. The 'bit twiddling' is correct.

The decode() method will only work for one format of audio files (little endian signed) so you will need to deal with other encoding.

One major problem you seem to have is in understanding what the results of the FFT mean. For that you need to spend some time learning about spectral estimation which means you will need a thorough understanding of Fourier transforms and in particular the Discrete Fourier Transform. I have a strong background in this and I can help but forums are very poor for '1 on 1' teaching of complex topics so you will need to spend a lot of time reading books and articles.

LenGrand Bibi

Greenhorn

Posts: 6

LenGrand Bibi

Greenhorn

Posts: 6

posted 4 years ago

http://en.wikipedia.org/wiki/Mel-frequency_cepstrum

I had never heard of the "mel cepstral coefficients" until you mentioned them so I can't help with that aspect. My music player only displays the short term spectrum but now I know it exists when I get some spare time I might try at some point to add to it a plot of the "mel cepstral coefficients".

LenGrand Bibi wrote:, if I suddenly want to here these results (after conversion) converted to mel cepstral coefficients, the fact that this should be done?

what it does take to do?

http://en.wikipedia.org/wiki/Mel-frequency_cepstrum

I had never heard of the "mel cepstral coefficients" until you mentioned them so I can't help with that aspect. My music player only displays the short term spectrum but now I know it exists when I get some spare time I might try at some point to add to it a plot of the "mel cepstral coefficients".

LenGrand Bibi

Greenhorn

Posts: 6

posted 4 years ago

Richard Tookey, Total my goal is to get the vectors MFCC ( I understand there are only 26 but it turns 13 )

The final path (If I understand correctly) is obtained as follows:

FFT ( we've already done it)) ---> mel transformation ( translate values that we received after the FFT in Mel ) ---> Discrete Cosine Transform ----> MFCC \o/

Approximately so)

What do you think about this?

The final path (If I understand correctly) is obtained as follows:

FFT ( we've already done it)) ---> mel transformation ( translate values that we received after the FFT in Mel ) ---> Discrete Cosine Transform ----> MFCC \o/

Approximately so)

What do you think about this?

posted 4 years ago

That pretty much follows the Wikipedia entry but the devil is in the detail. You will need to know how to to work out the relationship between the FFT bin number and the frequency, how many points to use for each FFT and how to implement the Discrete Cosine Transform (DCT). All this before getting to the actual MFCC.

Note - though not the most efficient method of computing the DCT, it is possible to use the FFT to do much of the work of computing the DCT.

Note - though not the most efficient method of computing the DCT, it is possible to use the FFT to do much of the work of computing the DCT.

LenGrand Bibi

Greenhorn

Posts: 6

It is sorta covered in the JavaRanch Style Guide. |