TalkBass Forums Semi-Parametric Equalizer?

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#1
09-04-2013, 04:19 PM
 Registered User Join Date: Jun 2010
Semi-Parametric Equalizer?

This I know is probably a very ridiculous question but what exactly does the semi parametric equalizer to and what do the level and frequency numbers mean? Here is a picture.
#2
09-04-2013, 04:24 PM
 Registered User Join Date: Apr 2008
It means you can cut and boost a band of frequencies centered about the frequency set by the "Frequency" knob, by an amount set by the "Level" knob. Because it is a semi-parametric you cannot set the width of the band of frequencies cut or boosted. That would take a fully parametric.

Last edited by Codger : 09-04-2013 at 04:27 PM.
#3
09-04-2013, 04:26 PM
 Registered User Join Date: Apr 2005
Not a dumb question. A semi-parametric equalizer allows you to shift the frequency (from the low mids through the high mids) with the cleverly named 'freq' control, and then, just like a normal midrange control, cut or boost that selected frequency center point with the level control.

The 'semi' part of the name 'semi-parametric' states that it is missing one control that a 'parametric' EQ has, and that is a Q control. The Q represents the width of the frequency range around the center point selected with the freq control.

So, a narrow Q means that the frequency range above and below the frequency selected is very narrow. Widening the Q 'fattens' that 'normal curve' looking frequency range impacted. Most semi-parametric circuits are set at a full octave, meaning they impact frequencies within the range of half the center point frequency below and double the center point frequency above. However, the farther you get away from the center point, the less the level control impact on that range of frequencies (again, think of the 'bell curve').

Hope that makes sense. The best way to hear this is to boost the level to about 3 o'clock, play an open A string, and slowly turn the freq knob with your other hand. You will hear that center point sweep from low to high and back. Try the same thing cutting the level to 9 o'clock.
#4
09-04-2013, 04:38 PM
 Registered User Join Date: Jun 2010
Oh cool! I've never messed with it because the signature Eden tone is so nice in and of itself but I'm getting some cool tones here from fat and boomy to warm and punchy to very thin and grinding. Cool. Does it serve any other purposes aside from the tone alterations? I've heard guys talking about dialing in for specific rooms, is this what they are referring to using to achieve such desired results? How can you tell which frequencies need to be cut or boosted based upon the room?
#5
09-04-2013, 04:44 PM
 Registered User Join Date: Apr 2005
Quote:
 Originally Posted by burns_isaac Oh cool! I've never messed with it because the signature Eden tone is so nice in and of itself but I'm getting some cool tones here from fat and boomy to warm and punchy to very thin and grinding. Cool. Does it serve any other purposes aside from the tone alterations? I've heard guys talking about dialing in for specific rooms, is this what they are referring to using to achieve such desired results? How can you tell which frequencies need to be cut or boosted based upon the room?
Yes, a semi-parametric mid is very useful for that. You kind of have to use your ear. For example, if you are on the floor of a big gym type venue (big open sound), it sometimes helps to boost the low mids (100hz-200hz) versus the bass control to clarify the low end. If you are playing on a raised hollow wooden stage which often causes the low end of a bass to boom and sound mushy, cutting in the 200-300hz region can often help).

Another example... if you are playing in a smaller room with lots of drapes, carpets, etc. that tend to eat up the top end of the sound, a slight boost around 1K or 2K can bring the brightness back a little bit.

No wrong or right answers, each room is different. Just remember that the term 'equalization' was really driven by the goal of keeping a rig sounding the same in different rooms... to keep the inherent tone you like sounding relatively the same from room to room.

Edit: When I owned my Eden WT heads with those multi-band semi-parametric section, the only thing I ever used that EQ for was slightly boosting or cutting low mids with the lowest band based on room acoustics. So, I hear what you are saying. Those are very nice heads, voiced very nicely for many players' tone goals right out of the box.
#6
09-04-2013, 05:49 PM
 Registered User Join Date: Jun 2010
You've been very helpful and I appreciate it! Thanks!

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