Posted on 
Apr 02, 2003 05:40 pm Heh, don't worry - that's not too much of a dumb question :)
A sweepable mid reffers to EQ. There are four main types of EQ:
1. Fixed EQ
Fixed EQ's are about as basic as you get - you'll often find these on cheaper / smaller mixers and they're designed to tidy up the sound rather than make delicate adjustments (think of fixed EQ's like a big old paint-brush). Fixed EQ's will be set to certain frequencies (on my Behringer MX3282a, the 4 stereo channels have Fixed EQ's set at 80Hz, 500Hz, 3KHz and 12KHz) - you can not change the frequencies at which Fixed EQ's operate. Fixed EQ's will only have one knob which sets the desired amount of Gain at the frequency labeled on it.
2. Sweepable Mid's
EQ with sweepable Mid's are the next step up from fixed EQ and they are found on the less expensive desks. They still have their Low and High frequencies Fixed (usually at 80Hz and 12Khz) - but have one or two EQ's which are sweepable - meaning that you can select the frequency at which the EQ's operate (on my MX3282a you can sweep from 100Hz to 8Khz) - these are obviously a bit more presice than Fixed EQ as you can choose the frequency you wish to foucus around. Sweepable EQ's will have 2 knobs - one to set the amount of gain you wish to apply and another to select the frequncy you wish to effect.
3. Parametic EQ
Parametric EQ's are the daddy when it comes to EQ! These are found on the more expensive consoles and allow for presice EQ'ing of signals. Again, they will usually have 2 fixed EQ's at 80Hz and 12Khz, but will then have 1, 2 ,3 or even 4 (on really big consoles!) Parametic EQ's. Parametric EQ's are fairly similar to Sweepable EQ's in the respect that they have an Amount Knob and a Frequency Knob, but they will also have a 'Q' knob. 'Q' reffers to the "width" of the EQ that you are going to apply. A small 'Q' value (reffered to as an 'open Q' will effect a large range of frequency around your selected frequency where as a higher 'Q' value (reffered to as a 'tight Q' will effect a much smaller area of the frequency range. For example, if you set the frequency knob to 2Khz and then boost using a tight 'Q', you will only affect the frequencies from 1.95Khz to 2.15Khz (this is just an example!) where as if you used an open Q you would probably affect frequencies from 1.3Khz to 2.7Khz)
4. Graphic EQ
Graphic EQ's are completly different to the other 3 types of EQ listed. They comprise of lots of sliders which represent the frequency spectrum from 20Hz all the way up to 15Khz. (some units have 32 such sliders, some have more, some have fewer). Graphic EQ's are not so much used on channels (like the other EQ's) but are more often used one the Main Outputs of a Mixing Console in a live situation to deal with any specific problems that are arrising. They can also be used to help compensate for known 'tuning' probelms within the mixing enviroment (eg: if you know there is a resonant peak at 120Hz in your mixing enviroment then you can take 2dB out of that frequency range without effecting the others.) Graphic EQ's can either be used to cut / boost specific frequencies, or the user can create a 'curve' to make more subtle changes to the character of the sound.
Hope that was helpful
jues.
