[Paul Frindle]

Originally Posted by Nishmaster

Ridiculous. The very fact that something cancels completely in a null test means by definition that it cannot possibly sound different.

Yes - if you arrive at exactly the same response, if all else is equal it cannot sound different. This is a logical reality. The point is how you reach your setting during creative use.

There is also another weird myth that I've seen propagating lately around here, and that's that somehow some eq's can exhibit more or less phase change than others. The way eq works is by altering the phase relationship between the original signal and the derived signal and adding them back together, thus producing a frequency specific change in gain.

EQ processing falls into 2 main categories infinite impulse response (IIR - where signal is fed back through a few weighted delays) and finite impulse response (FIR - where signal is fed through a great number of weighted delays but never fed back again). Combinations of both are possible to save processing under some conditions

The sort of EQ that most closely matches analogue (and the real world) is the IIR feedback versions. These produce the expected phase shift wrt freq response and gain similar to analogue EQ and other freq sensitive stuff in the natural world.

A more recently offered variant of EQ is the FIR feed along type model, which can produce arbitrary phase/freq responses (any phase relationship is possible) - with a correspondingly unnatural/novel impulse response over time. So called phase corrected (or phase linear) EQs are a version of this, most often consisting of a conventional IIR followed by an FIR to correct the phase shift (kind of doing the IIR in reverse). Such EQs must have a very significant latency because gaining a correct freq response at LF and high Q requires an impulse response that lasts a very long time - with the peak ages after the signal stimulus. They can also sound distinctly odd because the sound of the preamble precedes the sound that caused it - and of course no amount of delay compensation can fix this softening effect on the events and timing within the program.

Given two equal eq settings (Q, Center Frequency, Cut/Boost), any two eqs will produce an identical phase response.

That depends on what you actually mean; same settings, or same responses? If you follow the links I posted you can see that for the different types of EQ on offer the actual response for any gain and Q setting is in fact different between the EQ types. In fact what the 'Q' value actually is presents a bit of a conundrum for an EQ that passes all freqs, since a 'Q' value is related to the bandwidth of a natural filter that aims for no output at DC and extreme HF.

The styles of gain/Q dependency are intentionally provided to give character to the operation of the EQ and provide the correct 'feel' and facility depending on what the job in hand actually is. For instance the type 2 EQ with it's sharper response in cut is ideally suited for drum EQ where you want to tightly control resonances, but still want to accentuate overall responses in a single EQ style.

One of the significant changes I made to the SSL E-series EQ to form the G-series version was to change this gain/Q dependency, so that a larger bandwidth was boosted (or cut) at lower gain settings. This gave the impression of a gentler more forgivingly musical EQ when operated by the user and encouraged a different artistic style. This was more in line with the changing fashions of the time which were moving away from the harsher sounds popular in the early 1980 - and the most significant cause of the characteristic sound of the console was in fact the gain/Q dependency of the EQ section and how people were using it.

Of course, in a digital world, the steep sampling filter will introduce ringing and pre-echo, but with many digital eqs oversampling internally, I would say that this problem is mostly academic.

The ringing has nothing to do with sampling rates - it is a direct result of the freq/phase response and the associated impulse response. An analogue EQ with the same response will do the same thing - as would a collection of swinging pendulums or acoustic cavities coupled to give the same roll-off :-)