Filters adding volume?

[JonasEdenbrandt]

I was just listening to a few tracks and checking them with a spectrum to try and learn something from them. Well while listening to RJ by Radio Slave i added abletons auto filter and the track started to clip. I switched to fabfilters ProQ and had the same problem. So the track clips just cause the EQ/Filter is there even though I havn't changed any settings in the EQ/Filter.

Is this because the track is mastered and running really hot? So the slightest change makes it clip? Is this a sign of bad mastering? I belive the track was on Running Back and they are pretty serious right?

[omnipresence]

It just goes to show that often plugins will not be transparent even when they're not actively affecting the signal. Well yes, if a signal was running hot (like most mastered audio is) then it only takes a small increase in amplitude to make it clip. I would say it's unlikely the perceived volume of the signal is changing though.

I have noticed what you're describing, both in this situation but also with simple eq-ing of samples. For example, if you take a bassy kick drum and start to filter out the low frequencies, up to a certain point the amplitude actually increases even though the perceived volume is the same. This wouldn't always be the case as it's dependant on the original frequencies, but I don't know why it happens.

[cecil]

cutting on one end of the spectrum is like 'making room' on the other end, so with filtering you end up boosting (other) frequencies.

also as you vary the cutoff frequency, you'll get different spots where the amplitude is boosted. I guess this has something to do with the complex phase-cancellations, introduced by the filter...

[hydrogen]

is there a resonance boost on your filter?

[damagedgoods]

Is this because the track is mastered and running really hot?

Yup.

Is this a sign of bad mastering?

No, peak levels have nothing to do with good or bad mastering. You'd probably get the same result with a peak-normalized track, and peak normalization is nothing but a master volume adjustment.

It just goes to show that often plugins will not be transparent even when they're not actively affecting the signal. Well yes, if a signal was running hot (like most mastered audio is) then it only takes a small increase in amplitude to make it clip. I would say it's unlikely the perceived volume of the signal is changing though.

I have noticed what you're describing, both in this situation but also with simple eq-ing of samples. For example, if you take a bassy kick drum and start to filter out the low frequencies, up to a certain point the amplitude actually increases even though the perceived volume is the same. This wouldn't always be the case as it's dependant on the original frequencies, but I don't know why it happens.

Right. Instantaneous amplitude and signal power are not always related. Shifting the phase of certain frequencies can alter both the appearance of a waveform and the height of its peaks without affecting the perceived level or power spectrum. Most EQs and filters have an inherent phase shift, so will affect the instantaneous time-domain peaks even if the frequency response curve (which shows only the gain across frequencies, not the phase) is flat.

IMHO, the importance of peak levels is somewhat overstated these days because of the obssession with making everything as loud as possible. It shouldn't be surprising that running a mastered (ie limited to -0.01dB and maybe a little bit clipped as well) track through some filtering should cause it to peak, because the idea of limiting the peak level of a signal is actually not really that meaningful. We only do it because there's an upper limit to the amplitude we can represent on any medium, and this limit is defined by peak levels rather than RMS, power or perceived loudness.

In any case, isn't the default preset for Auto Filter a LPF with some resonance? Any kind of resonance DOES indicate more than 0dB gain at a certain frequency and IS likely to cause an increase in the amplitude if there's any signal content at that frequency (probable in a fully mixed track).