Harmonic analysis Equalize2

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KVRer
27 posts since 6 Dec, 2004

Post Tue Nov 09, 2021 1:38 pm

I was quite surprised to watch some noise (under -180dBFS) in plugindoctor when comparing to other eqs .
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KVRAF
5363 posts since 28 Dec, 2015 from Hanover, Germany

Post Tue Nov 09, 2021 1:47 pm

How does it sound? Good?

KVRer

Topic Starter

27 posts since 6 Dec, 2004

Post Tue Nov 09, 2021 1:52 pm

Acon equalize is an excelent tool. i love it. I just did a quick test on plugin doctor and noticed that. just wondering why. nothing else :D

KVRAF
1788 posts since 14 Sep, 2004 from $HOME

Post Tue Nov 09, 2021 1:56 pm

Just a wild guess, as I am no DSP developer:
Could it be truncation distortion? All these EQs will do their internal calculations in 64 bit, but maybe Equalize2 doesn’t support the doubleProcessing method (or whatever it is called) of the VST spec, so the 64bit get truncated to the 32bit output. Just a wild guess.
Anyhoo, as the noise is way below that of the analog components of your converters, it won’t really matter.

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KVRian
1237 posts since 1 Jan, 2005 from Norway

Post Tue Nov 09, 2021 11:25 pm

Please be aware that 200 dB range is a very extreme range and that the distortion levels here will never be audible. A 24 bit audio file has 144 dB dynamic range, so the truncation to 24 bit will mask this noise anyway. The technical reason for the distortion is that Equalize uses 32 bit FIR filtering. Many equalizers use IIR filters where 64 bit is a definite requirement because noise builds up in the feedback. This is not the case with FIR filters, where 32 bit is sufficient for high end audio.

Best,
Stian

KVRAF
6582 posts since 12 Feb, 2006 from Helsinki, Finland

Post Wed Nov 10, 2021 12:17 am

stian wrote:
Tue Nov 09, 2021 11:25 pm
Please be aware that 200 dB range is a very extreme range and that the distortion levels here will never be audible. A 24 bit audio file has 144 dB dynamic range, so the truncation to 24 bit will mask this noise anyway. The technical reason for the distortion is that Equalize uses 32 bit FIR filtering. Many equalizers use IIR filters where 64 bit is a definite requirement because noise builds up in the feedback. This is not the case with FIR filters, where 32 bit is sufficient for high end audio.
Yeah, what we see here is just the normal quantization noise of 32-bit signals. It doesn't even take any processing whatsoever, just convert any 64-bit signal to 32-bits before sending to FFT and it'll show roughly similar noise floor... yet it's still way more accurate than anything any physically plausible DAC will ever be able to output.

edit: Also not all IIR filters are created equal. Direct forms are notoriously bad, but implicit trapezoidal filters (better known as ZDF filters) can be perfectly usable in 32-bit as well (with slightly higher noise floor than what's visible here, but not so much that it'd make any practical difference).
Preferred pronouns would be "it/it" because according to this country, I'm a piece of human trash.

KVRer

Topic Starter

27 posts since 6 Dec, 2004

Post Wed Nov 10, 2021 2:11 am

Thanks for all replies. I´m a wiser person now :D eheh

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KVRian
1237 posts since 1 Jan, 2005 from Norway

Post Wed Nov 10, 2021 2:43 am

mystran wrote:
Wed Nov 10, 2021 12:17 am
edit: Also not all IIR filters are created equal. Direct forms are notoriously bad, but implicit trapezoidal filters (better known as ZDF filters) can be perfectly usable in 32-bit as well (with slightly higher noise floor than what's visible here, but not so much that it'd make any practical difference).
Thanks, your're right. I have only experimented with bi-quad structures, but there are surely better topologies to avoid noise accumulation.

Best,
Stian

KVRian
588 posts since 4 Jan, 2007

Post Sat Nov 27, 2021 5:01 am

Not that I understand all that, but leaving the papers for the trapezoidal SVF:
https://cytomic.com/index.php?q=technical-papers

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KVRian
1237 posts since 1 Jan, 2005 from Norway

Post Thu Dec 02, 2021 6:52 am

rafa1981 wrote:
Sat Nov 27, 2021 5:01 am
Not that I understand all that, but leaving the papers for the trapezoidal SVF:
https://cytomic.com/index.php?q=technical-papers
Thanks for the links! I'm afraid that these filter topologies don't give us the flexibility we need for Equalize, though.

Best,
Stian

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