Parametric vs Graphic – Equalisation with knobs on!
Already struggling with terminology? For those who are, I will start by telling you that “equalisation” is simply a posh term for tone control. Sometimes these appear as bass and treble on audio equipment but in a car, this is never adequate in order to tailor sound to match the listening environment.
Since the early days of car audio, the graphic equaliser was the weapon of choice for those looking to “correct” the sound of their stereo and make it more palatable. The advantage it gives over a plain old tone control or bass and treble is that it offers adjustments at several specific frequencies. The number of specific frequencies is dependent upon how accurate the adjustment needs to be as well as the cost and size required to accommodate a control for each frequency.
The image above is of a 2-channel 31-band equaliser as you may find in a recording studio or more typically these days in a PA set up. each slider enables the user to boost or cut the level at one of 31 specific frequencies. This type of equaliser offers the user a graphical representation (frequency against level) of what adjustments have been made and in the case of live sound mixing allow an engineer to immediately grab a frequency which may be causing a problem – such as a microphone feeding back – and reduce its level to make the horrible noise go away! In days gone by, the car graphic equaliser was limited by purely physical constraints such as size and cost. There are inherent issues with this kind of equalisation which dictate the use of very good quality components matched with exceptional design skills to ensure the unit does not simply add to the problems the user is trying to overcome. The lower the number of frequencies available for boosting or reducing the more problems ensue. In my experience anything less than 16 frequencies is pretty much a waste of time for those looking for detailed adjustment. Each control will not only act on its specific frequency but will also affect the level of adjacent frequencies so, you can see that the more controls there are, the more accurate the adjustment is going to be.
Audison’s Bit One features a 31-band graphic on each of its input channels. This offers extremely fine adjustment to be made and as in this case, it is all done in the digital domain via a laptop, the cost and size implications have been much reduced!
This kind of equaliser offers huge benefits over a graphic equaliser as it allows adjustments to be made to three separate parameters. In the case of the parametric equaliser in Audison Prima amplifiers, the user can make adjustments at up to 10 different frequencies – So, that’s less isn’t it? How can it possibly be as good? I hear you ask.
Ah well you see, in this case we are able to adjust our specific or centre frequency for adjustment. We can then boost or cut the level as with a graphic but we can also adjust the bandwidth or number of frequencies on either side of the centre frequency we would like to affect as well as by how much in proportion to the centre frequency. The latter parameter is known as Q or Q factor and this offers the parametric equaliser a lot more flexibility and accuracy. Once more, a physical box such as the typical pro audio one pictured above needs lots of knobs on it but with a software driven user interface, you can make all the adjustments you need with a mouse or buttons on your laptop. In fact, modern computer driven parametric equalisers are so sophisticated, they allow the user to drag a frequency up and down the screen as well as from left to right to adjust centre frequency and level in real time so you can hear the effect of your tweaking! The variable Q allows frequencies to be overlapped to iron out any transitional distortion or odd gaps between those frequencies being operated on allowing precise smoothing of the resultant sound curve.
As always, such devices require experience and decent ears. EQ can be as destructive as it can be helpful in the hands of the novice. Just take a look at the eq settings in your own car. Is the bass turned up full? have you taken all of the high frequencies out? – It often is in cars I listen to that have been set up by the inexperienced. Good equalisation should be extremely subtle. if you have to boost a frequency or set of frequencies to maximum or reduce them to minimum this probably points to a fundamental issue with your system and I would strongly recommend you visit your local FOUR MASTER and allow them to advise or adjust using their vast experience.