understanding a BBE 386 and a Parametric EQ

[dadroadie]

Hi to All,
If this is posted in the wrong section please let me know and I’ll try to move it to the correct one. I recently picked up a used BBE 386 Acoustic preamp to use with several of my acoustic instruments that only have passive piezo or under saddle pickups. The preamp section and the BBE process section were very easy to understand and have added a lot to the sound. I’m having trouble understanding the Parametric EQ section (number 6-7-8) on the (attached instruction). Could anyone that has a 386 possibly give me a better understanding of these controls and a good starting set points? Or if you know how a Parametic EQ works and what these controls do and how to adjust that would be very helpful. I hate to plead stupid but this forum has always been a great source of talented people helping others with less understanding. Thanks in advance! Dadroadie
BBE controls.pdf

[The Dude]

The parametric on this amp is basically 2 parts.

The first is knobs 6 & 7. Knob 7 adjusts the frequency of the filter and 6 adjusts the gain at that selected frequency. In my opinion, the best way to adjust this is:

1) Turn the level up full or nearly full level.
2) Adjust the frequency until it is most annoying and targets the frequencies you don't want.
3) Turn the level back down until you are satisfied that the offending frequency is cut to a level you like.

The second is a simple hi Q notch filter which simply cuts a narrow band of frequencies around the selected frequency. I find that typically around 200-300 hz is where acoustic guitar likes to feed back, but each amp is different, so you can adjust it to your taste, or not use it at all. Its probable best use is going to be to cut low and/or low mid feedback, so you can engage the filter and turn the knob until feedback goes away. If you have no feedback, you don't need it. But, it can still be used to tailor the low end to your liking.

[dadroadie]

Thanks for the reply! You gave a really clear answer on the controls. I'll give it a try other the weekend and let you know.
Regards
dadroadie

[Brad1]

The eq on that is more like a 'semi-parametric eq'. A fully-parametric single-band eq would have at least one more knob, for 'width'. The eq on the BBE is not much more than you couldn't do on a graphic eq, which you are probably familiar with. (All the sliders at ascending 'fixed' frequencies).

The eq on the BBE (disregarding the notch filter, for now) is basically a target EQ, to zero in on a problem frequency to narrowly-lower it, or boost a particular frequency you may want to accentuate for some reason...(like to cut through the band's volume?) It appears its width (frequency range of operation) is set to a certain set bandwidth, but its actual center frequency is 'sweepable'. The gain is to boost or decrease that center frequency, which smoothly ramps up and down around it with a boost, or down and up around it with an attenuation. At both ends of the fixed bandwidth, the signal should then be flat above and below it.

To imagine it using a more-familiar graphic eq, set all the sliders to center. Push up the center slider (say, 1K) about halfway to the top, then equally above and below it push those up halfway relative to previous ones until you have a nice even curve. You've just boosted the center frequency with both ends of it ramping up and down to 'flat', with the rest of the sliders (frequencies) flat and unaffected. The parametric curve from the BBE ramps up and down those frequencies either side of the center automatically, and leaves higher and lower frequencies unaffected.

A 'fully-parametric' EQ would allow you to also adjust the working bandwidth around the center frequency. Using your graphic eq, if you were to widen the bandwidth, you might start from the center frequency, and equally on both sides, set the neighboring sliders only about 1/4 of the way (up or down) from the next one. When you do that, you'll end up moving more sliders, with a wider frequency 'range' that is affected around the center frequency. Conversely, if you wanted to narrow the width, you'd be more aggressive around the center frequency, and bring the sliders down more quickly, in succession, and use fewer sliders either side of the center frequency to hit 'flat'.

The advantage of a parametric is that it can bring up or down a narrow or wide band smoothly and automatically. Getting too narrow on a graphic can get ugly, fast, because it's possible to attenuate many frequencies adjacent to each other, since each slider is a fixed frequency with a fixed width. If you push up, say, 1K, all the way, and then barely push up, say 630 below it, and 1.6K above it, you'll have some nasty hash. A parametric electronically and more-smoothly ramps up and down the frequencies around the center frequency.

The BBE 'parametric eq' function appears not to be able to control the width of the bandwidth. It can only control a 'set bandwidth', by 'sweeping' the center frequency with the frequency knob, and then adjusting its gain (or attenuation) with the gain knob. Using the graphic EQ again, if you have the 1K slider up and the surrounding sliders gradually going down, either side, to '0' (flat) on the eq, you could 'sweep' the frequency UP by taking each slider to the right of the 1K slider and adjusting them proportionately to the one to the left, now slightly introducing the next higher up frequency slider. The 1K slider would be lowered the one that was previously to the left, and each one next lowered proportionately, with the previous furthest-left one now set to '0' (flat). You have just 'swept' the center frequency, and all the others adjusted accordingly. A parametric does that automatically.

The 'notch filter'? A notch filter is specifically-designed to aggressively and sharply attenuate a narrow frequency. It appears the BBE can also 'sweep' the frequencies for that to find the offending one (the feedback from the monitors/PA/room that vibrates the guitar, transferring those to the pickup/mic back through the monitors, etc.)

It may have its own set bandwidth (range of frequency width), different from the width of the EQ section? I don't know. It is, however, adjustable to find the center of the offending frequency, and it's only function is to attenuate it, with a control over the level of how much.

What I also don't know with that particular device is...is it an 'either/or' device, or can both be set and used simultaneously? In other words, if you tweak in the 'parametric eq' function to sound very good, but still get a slight feedback, if you switch in the 'notch filter' and zero in on the feedback...did that leave your carefully-crafted parametric eq sound alone (besides notching out that particular feedback), or did it obliterate all that work, and the eq section is now useless? I'd HOPE they'd work with each other, and the notch filter was only added as a 'last resort' remedy? I don't know.

As far as the BBE Sonic Maximizer section, I think those basically do a very subtle 'frequency time realignment' between lows and highs. I believe the theory behind it is that higher frequencies travel faster than lower ones, especially out of PA speakers, so by a VERY short delay of the highs, it creates more of a subtle psycho-acoustic effect of having more 'punch', or 'immediacy' or 'clarity'...or whatever they claim. Gotta be careful with it, though, because using it too aggressively may cause 'phasing' issues, and it can get noticeable. They DO change the sound slightly, but can get kinda grating if used improperly. Those rack mount Sonic Maximizers were kind of popular in the 80's, as well as the other popular rack mount sound manipulator, the Aphex Aural Exciter. I've actually still got one of each around. The Aphex worked differently. It actually kind of introduced a slight purposeful distortion and overtones into the highs...to 'smooth them out', or whatever. That thing actually came in kind of handy when transferring some old tapes to digital. Diminishing highs of old tapes, already, it did help brighten them up slightly. Anyway...enough about that.

So, that's pretty much what a parametric, a notch filter and a sonic maximizer is, what they do, and what they're used for...as opposed to the familiar ol' graphic eq. Scads of articles online can explain all this more thoroughly, and with pictures! Understanding what that thing really does should help you reap any benefits of using it properly, and avoid any pitfalls of incorrectly using it. (Like...ear-piercing squeals, muddy sound, or just plain grating sound.)

Good luck!

[dadroadie]

Thanks for the GREAT info! I'll try all this out over the weekend and keep you posted.
Regards dadroadie

[Helmholtz]

I believe the theory behind it is that higher frequencies travel faster than lower ones

I don't know how the BBE Sonic Maximizer works but the speed of sound does not change with frequency.

[Enzo]

You are right, it doesn't. But drivers are rarely time aligned on PA speakers. The voice coil on the tweeter is right near the baffle, while the voice coil of the woofer is maybe 8-10 inches further back. If you delay the highs slightly, then they are sent out more in alignment with the woofer signal. I kinda think that was the underlying idea in Brad's remark.

[Brad1]

You are right, it doesn't. But drivers are rarely time aligned on PA speakers. The voice coil on the tweeter is right near the baffle, while the voice coil of the woofer is maybe 8-10 inches further back. If you delay the highs slightly, then they are sent out more in alignment with the woofer signal. I kinda think that was the underlying idea in Brad's remark.

Yeah, I did oversimplify the Maximizer things a bit with the 'speed' thing. It does try to do some frequency time alignment, and it has to do with different arrival times...possibly because of what Enzo said.

Been a long time since I read about these to figure out how to use it. Here's a basic different (but similiar) basic explanation from SOS.

https://www.soundonsound.com/reviews...maximizer-plug