This version (18 May 2021 08:43) was approved by John Joseph.The Previously approved version (02 Jul 2020 15:36) is available.Diff

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N-point FFT is performed on the samples, where N is configurable and should be a power of 2, greater than or equal to 16. The twiddle coefficients are calculated within the code and output is given as PCMx samples, the BlockSize of which is 3 * Schematic Block Size. The first Schematic BlockSize number of samples in a PCMx output contains the header information to be carried on to the next Module (say in this case IFFT). The header information contains fields such as PCMx type (Windowing done), N, Count (if N>Schematic BlockSize). Since memory size depends on the value of N, downloading the Schematic (Link-Compile-Download) is necessary when N value is changed.

FFT Windowed

In the Windowed FFT version, Raised Cosine window is used for windowing samples. Windowing is done for samples before calculating FFT and ‘overlap and add’ is done after IFFT. Here the windowing is done for 2N samples and therefore FFT done for 2N samples.

Real FFT

Real FFT is a block processing module which computes the FFT of real signals. It is for reduced memory and Mips.

Complex FFT

Complex FFT is a block processing module which performs N point complex FFT of the input signal, where N stands for BlockSize.


  • FFT
  • FFT Windowed
  • Real FFT
  • Complex FFT

Targets Supported

Name ADSP-214xx ADSP-215xx/SC5xx ADAU145x/146x
————————————-- ——————-- ——————————-- —————————-
FFT Windowed NA B NA
Complex FFT NA NA B



Name Type Description
———————- ————-- ———————-
Input0 Audio First Input channel (FFT and FFT Windowed)
Input1 Audio Second Input channel (FFT and FFT Windowed)
Input Audio Input channel (Real FFT and Complex FFT)


Name Type Description
———————- ————-- ———————-
Output0 PCMx First Output channel (FFT and FFT Windowed)
Output1 PCMx Second Output channel (FFT and FFT Windowed)
Output Audio Output channel (Real FFT)
Output Complex Output channel (Complex FFT)

Configurable Parameters

GUI Parameter Default Range Function Description
—————————- ———————- ———————————————- —————————————-
N 64 16 - 1024 N-point FFT to be performed. This should be value greater than 16 and a power of 2.
Alpha 0.1 0.1 - 0.9 alpha in the Raised cosine window function
ApplyScaling True True or False Whether scaling to be applied
Implementation Mips Optimized Mips Optimized / Memory Optimized Implementation to choose from

DSP Parameters

Name Description ADSP-214xx/215xx/SC5xx ADAU145x/146x
—————————- —————————————————————————————- —————————- —————————-
N N-point FFT to be performed Integer NA
InvWS 1/(2*N - 1) needed for calculating window coefficients Float NA
Inv1MinA 1/(1 - alpha) needed for IFFT to get back the original signal based on alpha Float NA
alpha alpha in the Raised cosine window function Float NA
resources/tools-software/sigmastudiov2/modules/advanceddsp/fft.txt · Last modified: 12 May 2021 13:20 by John Joseph