Convolution reverb on SigmaDSP

Hi Kevin,

I would imagine this could be easily implemented on the ADAU145x for fairly long impulse responses. Either as a rather large sample-by-sample FIR filter, or using some sort of Block Convolution/Overlap & Add Method with the FFT block (block processing).

The limitation on the filter impulse response length would be the amount of available internal DM0 or DM1 memory, which is:

20K words per DM block for the ADAU1452

8K words per DM block for the ADAU1451

4K words per DM block for the ADAU1450

-JT

Hi JohnTo,

Thanks for your answer! "20K words per DM block".. does one word correspond to one audio sample?

Gr. Kevin

Hi Kevin,

1 word in memory would correspond with 1 24-bit audio sample. So 20,000 memory words would be less than 1/2 second (at 48 kHz sample rate) if you were only doing FIR filtering and nothing else.

Thinking about this some more, you probably might want some reverb responses that is a few seconds long. If so, then a higher end processor like a SHARC DSP with fast external DDR SDRAM memory would be preferable. For an architecture like a Sigma300, realistic artificial reverberation could instead be achieved with IIR first and second order all pass/comb/lattice filters, etc.

Still, the ADAU145x can offer the ability to execute a fairly large FIR filter. I just realized the FIR block allows a maximum 10K per filter. Four FIR filter taps can be accessed in a single instruction cycle with the quad 32-bit multiplier, which means the 10K FIR filter would execute in 2500 cycles. I would imagine you can combine parts of a larger response using multiple FIR filters.

I just did a quick test of a 10K FIR filter and got a cycle count of 2565 total cycles including the filter and audio framework, or 42% of the 294 MHz processor bandwidth at 48 kHz fs.

-JT

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