Convolution with Null filters are audible

[alec_eiffel]

Buf i

On 11/25/2018 at 7:34 AM, flkin said:

Update on Roon convolution. Looks like there is indeed a bug in the convolution module in way resampling filters are handled. Alex Eiffel in the Roon communities found a way to measure the problem and deduced the issue.  CTO Brian from Roon Labs accepted his reasoning.

 

Full details are here in message 137.  

https://community.roonlabs.com/t/convolution-with-null-filters-are-audible/51732/138 

 

but probably safe to say this will eventually be fixed in Roon eventually. Convolution might be usable after all! ?

 

Brian comitted to look into it and fix the bug in one upcoming version of Roon (no deadline given). 

In the meantime make sure your convolution .zip file contains filters at all the frequencies you are playing, as Roon is improperly resampling them. Or use another convolution engine such as HQPlayer or Jriver.

[alec_eiffel]

Bug has been fixed in Roon 1.6.

[alec_eiffel]

By precaution I would keep convolution filters 32 bits or more. 

Maths shot from the hip:

- assuming 100000 tap filter

- implementation in the time domain 100000 multiplications, 100000 additions

- quantization noise grows proportional with square root of operations. I guess this coeff of proportionality is somewhere between 0.2 and 1. So 0.2x sqrt(100000+100000) = 90, thereof 6-7 bits “eaten” by the various operations. A 24bit file will turn into a 17-18 bit file, maybe worse.

Of course in real life, convolution is implemented through fast convolution and DFT, so maybe ultimately the addition of quantization errors is not as bad, but why take the risk ?

My 2 cents