How many eq bands do you need?

There are two kinds of equalizers – graphic equalizers, and parametric equalizers.

Graphic EQs only allow you to change the gain of each filter – but they do also let you draw a happy face.

The center frequency and the bandwidth for each filter, or “band”, are decided by the product designer. If the graphic EQ is a 31-band graphic EQ, the bands are at ISO standard center frequencies with a standard bandwidth (Q = 4.4). This reduces interaction between adjacent EQ bands.

Parametric EQs let the user define the gain, bandwidth, and center frequency parameters for each filter. For this reason, parametric EQs are the choice of experts — because we can choose the center frequency and the bandwidth needed to solve each problem!

Our first two Audison bit DSPs had 31-band graphic EQs on every output channel. One of those DSPs, the bit Ten, is still in production today.

Our latest, fourth-generation bit DSP amplifiers have 15 EQ bands on each output channel, with parametric control — in addition to 12 input EQs (12 bands each) and a global EQ with 70 effective EQ bands!

Is it really necessary to have 31 EQ bands?

It is indisputable that a 15-band parametric EQ is more powerful a tool for tuning than a 31-band graphic. It’s not even a question. But we still get this request.

Why? Well, our first expectation was that this person must have been running out of EQ bands – but as any experienced vehicle tuner already knows, it’s hard to use 15 parametric bands, especially in fully-active systems. Needing 31 bands per channel in active systems is just unimaginable! Neither the tweeter, the midrange, the midwoofer, nor the subwoofer channels will cover enough notes to need that much work.

As experienced tuners also know, EQing narrow dips in the response above 1500 Hz is a waste of time – especially if they were detected with a single-mic stationary measurement. An inexperienced tuner might feel that they want to do a really good job and get a ruler-flat response by chasing those narrow dips above 1500 Hz, but these dips are really inaudible to us (since they change frequency as our heads or mics move slightly, our brains already know to ignore them).

So why do people ask for 31 bands per channel?

We have wondered this for years, and I used to think that people couldn’t handle parametric EQ, and needed the simplicity of graphic EQ. That’s why we had the Graphic EQ mode in bit Drive – but we still got the complaint.

We think we finally have this sorted. It turns out, these users aren’t really asking for 31 bands, and they aren’t scared of parametric EQ controls. They want the EQ bands to already be in the right locations, and the easiest way to do it is to place them on the familiar 1/3 octave center frequencies, so they don’t have to be moved around! The benefit of a parametric EQ is the opportunity to choose the center frequency, but these users are asking to not have to make that choice (they may or may not know it, but they want that 4.4 bandwidth value as well).

They want it ready to go!

The ISO standard frequencies are exactly what you see in the user interface for the original bit One EQ: 20, 25, 31, 40, 50, 63, 80, 100, etc, etc. 

So, shouldn’t we just “listen to the market” here?

Our hardware limitation here is that we have already used over 100 biquad digital filters for our OEM-correction input EQ (12 bands for each of 12 input channels), and nearly another 100 for our global tuning EQ (5 controls, replicated on each of 14 output channels).

That doesn’t leave enough DSP resources to deliver 31 bands that we don’t really need, on each of 14 output channels. In the image to the right, you can see how the default center frequencies aren’t that helpful with fully-active systems.

What do we do? Do we install 31 bands, even if it means we take capabilities away from our industry-leading OEM correction EQ tools? Not an option – in that area, 12 is barely enough. Eliminate our very popular and useful global EQ? Not doing that, either – users switching from products without a dedicated global EQ tell us how much they love ours.What do we do? Do we install 31 bands, even if it means we take capabilities away from our industry-leading OEM correction EQ tools? Not an option – in that area, 12 is barely enough. Eliminate our very popular and useful global EQ? Not doing that, either – users switching from products without a dedicated global EQ tell us how much they love ours.

What we have done is introduce two new features

Full Time Graphic Mode

With bit Drive prior to 2.1, in Parametric mode, each output EQ filter was visible across the bottom of the screen, and each was controlled by a single interface element box with three controls: Vertical gain slider, rotary Q/bandwidth knob, and rotary center-frequency knob. To use the EQ band, you selected the desired band by clicking on it, then you used the controls within the box. The default bandwidth was 2.2. If you wanted to change the band’s function from EQ peak (the default) to shelf, notch, or all-pass instead, you did that by clicking on the button for that band, and selecting the desired filter type. Then the 3-element control box would change to present the appropriate controls (notch filters and all-pass filters don’t need a gain slider, first-order all-pass filters don’t need a “Q” adjustment, etc).

If you changed the EQ to Graphic mode, now you were presented with 15 gain sliders, with fixed center frequencies and fixed “Q” bandwidth. Now you had no access to the other filter types listed above.

With bit Drive 2.1, we now show 15 gain sliders at all times (see the image below).The three-element control box now loses its gain slider, and now just has two rotary knobs.

We have removed the Graphic/Parametric toggle button, and the default bandwidth is still 2.2. This makes the EQ easier to use, especially if the center frequency of the EQ band happens to be at the desired frequency.

But with 15 bands spread out over the 20-20k range, what are the odds of that? Read on!

Dynamic Band Assignment

We replaced the Graphic/Parametric setting with the Dynamic Band Assignment button. When you click this button and confirm the action, bit Drive checks the crossover frequency for the selected channel. Based on the crossover frequency, DBA will change the center frequencies of all 15 bands to cover the range required (this focuses on the passband, but is not solely limited to the passband – sometimes stop band EQ is required, of course).

For fully-active 4-way systems, DBA will cover all needed frequencies within each channel (tweeter, midrange, midbass, and subwoofer). For active 3-way systems, with a 6.5 playing from 80 to 2500 (for example) DBA can’t quite reach 1/3 spacing on the woofer, but it’s close.

The default for DBA is 1/3 octave spacing – the same spacing used by bit One and bit Ten 31-band EQs. The default “Q” changes from 2.21 to 4.4 (the default “Q” for 1/3-octave EQs) to reduce filter interaction.

At this time, DBA is a channel-by-channel selection. There is no global setting for all 14 output channels but we will add one soon!

If you select DBA accidentally, you can reset the EQ bands to their default values with the reset EQ button for that channel.

It actually does save time!

I’ve now used Full-time Graphic Mode and DBA while tuning several cars.

I have found that those requesting 1/3-octave spacing actually have a point – in modern multichannel systems, it does save me time to have all the bands I need already be in the passband for each channel.

Otherwise, I’m spending time on each channel moving a lot of EQ bands into the right spot.

I’ve never needed close to all 15 bands in any situation, but I’m certainly glad to have had the tools I needed already in position – without losing any crucial capabilities in our Input EQ or Global EQ.

Give Dynamic Band Assignment a try next time you tune with bit Drive – I think you’ll be glad you did!