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Forums     Discussions     Free Audio Plugins SPAN and frequencies below 20 Hz

I use SPAN daily in my mastering work, and recommend it to all my clients running Windows.  I notice that a lot of recordings have huge "tails" below 20 Hz.  Some EQs, like Waves, or the low cut in Elephant, will remove it.  Others, like Algorithmix PEQ Red, won't touch it.  In fact, with the PEQ Red I can use a low cut filter as high as 1 KHz, and it simply won't affect the frequencies below 20 Hz.

My question is, is there really information down there that should be filtered out, or is it just an inaccuracy in measuring those frequencies?  I set the SPAN block size to 8192.  Any ideas why Algorithmix doesn't affect it while other EQs do?  I prefer to use Algorithmix whenever possible.

Thanks for your help!

Brian Hazard

Resonance Mastering

I can't say much about PEQ Red, but if that bothers you I suggest asking for advice from the developer of PEQ Red.  To my knowledge, filtering out lower frequencies is an easy task, in DSP terms.

Frequency content at lower frequencies is measured by SPAN correctly for the given block size.

That is very odd, as I use Algorithmix PEQ Red to filter out anywhere from 30-39 Hz down to DC and the cut shows up on Span's FFT (as well as Izotope Ozone's FFT); granted, it is not a major cut, and does not quite mathematically match the cut amount on the eq.  On the other hand, I usually use a low-shelf with a high Q as opposed to a low-cut filter.  You can also stack more than one low-cut and/or low-shelf filter if needed.

The phenomena may have something to do with PEQ Red's FIR linear phase frequency domain process; perhaps it is not as effective in the lowest frequency ranges; perhaps the 'aural perception' of a less drastic cut due the LP nature somehow translates to the FFT graph (via the binning/block size?).  Incidentally, what quality setting do you use on the Red, Brian?

P.S.  When I demoed the Orange, it had a stronger LF cut than the Red, but did not sound as sweet.

George Piazza

Virtual Audio Mastering, Mixing & Recording

George Piazza - - Mastering, Mixing, Restoration - 'Supernatural Horror' = Music, Sound Design - progressive rock group

Hi George,

Peter of Algorithmix explained that the PEQ Red, and supposedly any linear phase EQ, can't knock out DC, because you need a filter for that.  I'd look up the e-mails to give you a more technical explanation, but I've since dumped and uninstalled Outlook.  I use the PEQ Orange when the DC is out of control, but only when I really have to.  It definitely doesn't sound as sweet as the Red for anything.

I always use the Xtra quality setting.  With the latest VST versions of the Algorithmix stuff, it barely even hiccups on realtime playback, even with a big stack of other plugs.


{+} Brian Hazard

{+} Owner, Resonance Mastering


{+} email:

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