Electronic – Lossless FFT on audio data

armaudiofft

I have an application where I'll be receiving an audio stream, much like using headphones, into my processor. I would like to run FFT and various DSP algorithms on the sampled audio and then spit the audio back out as if the device wasn't there. Basically doing DSP in real-time in between samples I guess. The processor I'm using is the MKL26Z128xxx4, mounted on the FRDM-KL26Z development board. It has a single ARM Cortex M0+ core and is programmed in C/C++ and can use the THUMB Assembly instruction set.

How would I do this without losing any of the streamed audio?

Best Answer

FFT needs to sample at at least twice the frequency of your signal, and should not introduce any loss. Loss is introduced on compression or encoding. Your input and outputs should be able to match the frequency, amplitude, and frequencies of the signal you are sampling.

Your biggest challenge is processing the DSP algorithms in real time, which depends on the algorithms you use, how many, and how your processor can keep up with it, with minimal delay. Like fractions of a second, to stay in sync with anything else (Video, other audio, or live instruments).

You need to do some calculations on what you need, through testing, before you can find out if your platform is good enough, or where you need to rethink or cut around.

Related Solutions

Simple playback audio with FFT not working (dsPic33F)

Perhaps it's an outdated answer. Anyway, the issue with your code is that FFTComplexIP store the result in the bitreversed order. You must add the

BitReverseComplex(7, &Frame[0]);

between the FFT and the iFFT function calls.

The following is written in the dsPIC Language Tools Library:

Remarks: N must be an integer power of 2. The elements in source complex vector are expected in natural order. The resulting transform is stored in bit reverse order.

Electronic – How to decode ARMv7 instructions

The ARMv7-M reference manual does not have a decode lookup table, but the encoding for each instruction is listed.

In the specific manual you have linked, you will find this in the section A6.7 - Alphabetical list of ARMv7-M Thumb instruction.

This contains - as stated - a list of every instruction, and their corresponding binary encoding. For example, page A6-16 has the binary encoding for the ADC (immediate) instruction. We can see that it starts with 11110... and spans two words.

The problem is going "backwards". The manual does indeed contain all the necessary information, but it is difficult to search. The disassembler has the data structures in place to do that for you, and if you want a table and do it manually, I suggest looking at the source code files for an ARM disassembler, for example GNU binutils.

Best Answer

Related Solutions

Simple playback audio with FFT not working (dsPic33F)

Electronic – How to decode ARMv7 instructions

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