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Old 10-07-2019, 10:54 AM   #1
Cup
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Default why does previously limited wav overdrive when EQ adjusted down?

I outputted a mastered mix as a wav, and put it on my website. Listening on other devices, I felt it was too bassy.

For long-winded reasons, instead of remastering, I brought the wav into a new Reaper project. I applied two instances of TDR Nova to reduce the low frequencies (one was a steep HPF at a v low frequency, the other a gentle HPF higher up). The thing went over 0dBFS, to about +2.

I sacked Nova, and tried ReaEQ. Same thing, although with slightly lower overdrive values.

All I've done is reduce some frequencies.

Without the EQ plug-ins, the track peaks at 0, as I'd expect, given that I set it there before outputting in the first place.

Any thoughts?
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Old 10-07-2019, 11:20 AM   #2
Lokasenna
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Filters don't just roll off - there's a resonant peak at their cutoff frequency. For low Q values (shallow), this isn't noticeable and they behave exactly as you'd expect. As you increase the Q you start to get a little bump, and at very high (steep) values it can be a huge spike.



The good news is that you can just turn the mix down to fix it.

Side note: IMO you shouldn't limit to 0dbfs anyway, because various formats will add a bit of level when you encode them. MP3s are particularly bad - I played with it a while back and if memory serves a 320k MP3 was adding 1db or so, all the way up to 4db at 128k.
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Old 10-07-2019, 11:41 AM   #3
Cup
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Ahh ... that's v helpful, thanks. I was wondering about just nudging the level down over all, but was worried in case something had gone bonkers. Cheers.
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Old 10-08-2019, 05:10 AM   #4
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Note that even without a resonant peak in a filter's response you can still get an increase in the waveform's amplitude. e.g. a square wave fed into, say, a 4th order butterworth (no peak) filter the increase can approach 2dB.

Of course, this applies to real circuits, not just software. Long before we had computers to simulate such things I used to demonstrate this to electronics engineering students.

To understand all this you need to understand Fourier analysis and phase shift in filters...
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Old 10-08-2019, 06:30 AM   #5
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Quote:
Originally Posted by Cup View Post
Without the EQ plug-ins, the track peaks at 0, as I'd expect, given that I set it there before outputting in the first place.
Beware that peaks at Zero db (or even much higher) within a DAW don't "overdrive" anything or hit any limit, It's just another mark in the dB meter, and does not harm at all (only at the point when rendering to an output file, but there you'll see a different display showing the results).

-Michael

Last edited by mschnell; 10-08-2019 at 12:12 PM.
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Old 10-08-2019, 09:22 AM   #6
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To add to the previously mentioned, an eq has many different possibilities of filters that it can be set at. And how much a resonant freq is raised when the set freq is lowered will vary from barely, if at all perceptibly, to a lot. If you change the band's type of eq you can see how differently they affect the surrounding freqs.
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