[DSK6713] issue with FFT and IFFT of C67x dsp library

Hayden Kim

Genius 15580 points

With DSK6713 (TMS320C6713), customer is using FFT and IFFT of C67x dsp library (dsp67x.lib).

They did below things.

* Audio Capture

* FFT [ gen_w_r2(w, N); bit_rev(w, N>>1); DSPF_sp_cfftr2_dit(x, w, N); ]

* IFFT [ DSPF_sp_icfftr2_dif(x, w, N); divide(x, N); ]

* Audio Playback

With above FFT - IFFT, original captured audio should be output, right?

But, actually there is no sound output.

Is there anything more required to do?

Thanks and regards,

Hayden

over 12 years ago

0 Rahul Prabhu over 12 years ago

TI__Guru** 116170 points

Even before you try to audio playback the the IFFT, can you plot the signal and see if it matches with the input buffer. The signal could be scaled so plot it to ensure it the waveforms look similar on the graph. I am assuming that you have tested the Audio pass through without the the FFT and IFFT before conducting this experiment.

Regards,

Rahul

0 Hayden Kim over 12 years ago in reply to Rahul Prabhu

TI__Genius 15580 points

Customer tested after replacing the FFT and IFFT of dsplib with C function calls, then the sound come out well.

(The C code is referred from the document of TMS320C67x DSP Library Programmer's Reference Guide.)

If the result data was scaled, some post processing of scaling will be required, right?

Regards,

Hayden

0 Hayden Kim over 12 years ago in reply to Hayden Kim

TI__Genius 15580 points

Is there example CCS project (with source code) of doing FFT and IFFT with the APIs of C67x DSPLIB?

Best regards,

Hayden

0 Rahul Prabhu over 12 years ago in reply to Hayden Kim

TI__Guru** 116170 points

Hayden,

I tried this out myself using the FFT example provided as part of the library and I see that the input signal is recovered by performing FFT followed by IFFT. There is slight difference in the precision but I don`t see any sort of scaling issues.

Regards,

Rahul

0 Hayden Kim over 12 years ago in reply to Rahul Prabhu

TI__Genius 15580 points

Thanks Rahul.

I think this may be from the input data align requirement.

Do you know what will happen if the input data is not aligned?

I will check with the data (x and w) alignment.

Regards,

Hayden

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[DSK6713] issue with FFT and IFFT of C67x dsp library