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espressif / esp-dsp

DSP library for ESP-IDF
Apache License 2.0
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Inverse of dsps_cplx2real_fc32 (DSP-99) #60

Closed ayavilevich closed 11 months ago

ayavilevich commented 1 year ago

Request for a feature or assistance.

I learned that an optimal fft of a N real input can be done using a full fft on an N/2 input and then a call to dsps_cplx2real_fc32 . I understand that an fft of a complex input/output can be used as an ifft with some small adjustments.

I am looking to do an efficient ifft where the output is expected to be real and the input is the same format that dsps_cplx2real_fc32 returns. Is it possible to do it in an efficient way like it is possible with the forward direction? Do we need an inverse of dsps_cplx2real_fc32 and then a call to a full fft with N/2 values? Please advise.

dmitry1945 commented 11 months ago

Hi @ayavilevich ,

the forward FFT is complex conjuction of inverce FFT. You can just make FFT that we have, calculate the result and and then multiply imag part to -1.

Regards, Dmitry