Is there such thing as dynamic EQ? For example I want to decrease 15-20 Hz to avoid port noise, but I want to decrease it only if it's above 80 db

[PashkaTLT]

Hello,

Is there such thing as "dynamic" EQ?

For example, I want to decrease 10-20 Hz to avoid port noise, but I want to decrease it only if it's above 80 db, because on low or normal volume I get quality ultra low bass without port noise.

Can I do this with miniDSP or Equalizer APO?

 

[NotInYourHead]

I suppose you're looking for a high-pass filter?
Edit: Compression too, as volume is increased you can limit bass SPL to a certain level, which should do what you're looking for. Not sure if it's built into miniDSP.

 

[Holmz]

Hello,

Is there such thing as "dynamic" EQ?

For example, I want to decrease 10-20 Hz to avoid port noise, but I want to decrease it only if it's above 80 db, because on low or normal volume I get quality ultra low bass without port noise.

Can I do this with miniDSP or Equalizer APO?

It is going to be lipstick on a pig whichever ay you go…
So maybe just hack away and put some aero port onto the existing thang?

 

[voodooless]

You’re looking for something called a multiband compressor. It’s basicly a frequency dependent dynamic compressor.

Some MiniDSP devices have a compressor, but it’s not frequency dependent. I don’t know about APO, maybe it allows you to do something clever?

 

[PashkaTLT]

It seems that what I need is called a multiband compressor or a dynamic EQ. Now I just need to find one that will work well in my case. I've just tried TDR Nova and while it works, the slope that I was able to make is very shallow, even affecting 100 Hz. I was not able to make it steep below 20 Hz (blue line is the dynamic EQ that's applied when the treshold is breached and yellow is static EQ):

 

[voodooless]

A very narrow EQ will have significant impact on group delay.

As to your image, it seems 2 filters are active. What is the second one?

 

[Holmz]

It seems that what I need is called a multiband compressor or a dynamic EQ. Now I just need to find one that will work well in my case.
…

That is still a bandaid fix, to address the bad design issue which is the port chuffing.
(Sure, one can stack workarounds on top each other.)

 

[ppataki]

Hello,

Is there such thing as "dynamic" EQ?

For example, I want to decrease 10-20 Hz to avoid port noise, but I want to decrease it only if it's above 80 db, because on low or normal volume I get quality ultra low bass without port noise.

Can I do this with miniDSP or Equalizer APO?

Fabfilter Pro Q-4 would be another excellent choice for the dynamic EQ

 

[Chris A]

A very narrow EQ will have significant impact on group delay.

Fabfilter Pro-Q4 and Pro-MB plugins. which I use fairly extensively for both playback and audio file editing, have three options for bandpass frequency filter type, one of which is linear phase. This allows the user to avoid added wild shifts in phase/group delay response near the loudspeaker port frequency due to a plugin attenuation/compression filter (which one gets with typical freeware plugins having only minimum phase filters).

Additionally, you can manually set the threshold of when the filters will kick in, which is another one of the apparent "wants" the OP mentioned.

That is still a bandaid fix, to address the bad design issue which is the port chuffing.

This is unfortunately true. If you are presently getting port chuffing with typical music tracks, note that these tracks have already been edited at mastering time to attenuate the bass response to avoid issues with loudspeakers having limited bass response capabilities (i.e., one-size-fits-all music tracks for all of us).

Probably the only way out of this situation is to add one or more subwoofers (or replace the subs you have if they are currently chuffing) that cover the frequency band of the loudspeakers having port chuffing issues.

Chris

 

[sigbergaudio]

Hot take: At low SPL you won't hear 10-20hz anyway, so you might as well just use a normal high pass.

 

[Chris A]

Hot take: At low SPL you won't hear 10-20hz anyway, so you might as well just use a normal high pass.

The problem with this is that "normal high pass" IIR filters add lots of very undesirable phase lag and a big jump in group delay (if high-Q). If your already flabby bass reflex bass response is paired with a high pass filter, it just gets flabbier. You need linear phase filters to keep the phase from going out of bounds. But note, you're looking at really large time delays at these frequencies (10-20 Hz), so if you're trying to synch with video, you may have a problem.

I recommend plugging the BR ports in your chuffing-port loudspeakers, and re-EQing the setup (i.e., just take the -3dB loss in amplitude response at the port frequency).

Chris

 

[Holmz]

Hot take: At low SPL you won't hear 10-20hz anyway, so you might as well just use a normal high pass.

But chuffing makes the frequency higher…

 

[voodooless]

Fabfilter Pro-Q4 and Pro-MB plugins. which I use fairly extensively for both playback and audio file editing, have three options for bandpass frequency filter type, one of which is linear phase. This allows the user to avoid added wild shifts in phase/group delay response near the loudspeaker port frequency due to a plugin attenuation/compression filter (which one gets with typical freeware plugins having only minimum phase filters).

You cannot really use linear phase filters for dynamic EQ without incurring signal delay. Because FIR is not time linear, it's always delayed, so you'll always be late in applying the EQ. You can mitigate this by delaying everything a bit more, then starting the correction before it should happen (so in the "future"), so that the resulting correction happens at the right time. I'm not even sure if you can do dynamic EQ with FIR? Most probably, the dynamic EQ is just a minimum phase implementation.

 

[ppataki]

I'm not even sure if you can do dynamic EQ with FIR?

In Pro Q-4 at least, you can, Dynamic EQ is also linear phase (if you enable Linear Phase mode in the plugin overall)

 

[voodooless]

In Pro Q-4 at least, you can, Dynamic EQ is also linear phase (if you enable Linear Phase mode in the plugin overall)

It seems it does, but it also notes the caveats, alluding to what I already described:

Linear Phase processing​

Dynamic EQing also works in Linear Phase mode, but only for Processing Resolution settings up to High. The attack and release response will be slightly different from the normal behavior in Zero Latency and Natural Phase modes.

When using dynamic EQ in Linear Phase mode in combination with the Very High or Maximum resolution settings, you will see a warning sign next to the Processing Mode button to indicate that this is not possible. In this case, simply lower the resolution to High or lower to be able to use dynamic EQing.

 

[sigbergaudio]

The problem with this is that "normal high pass" IIR filters add lots of very undesirable phase lag and a big jump in group delay (if high-Q). If your already flabby bass reflex bass response is paired with a high pass filter, it just gets flabbier. You need linear phase filters to keep the phase from going out of bounds. But note, you're looking at really large time delays at these frequencies (10-20 Hz), so if you're trying to synch with video, you may have a problem.

I recommend plugging the BR ports in your chuffing-port loudspeakers, and re-EQing the setup (i.e., just take the -3dB loss in amplitude response at the port frequency).

Chris

Yes, just stuffing the port is a useful idea as well.

 

[Ramon Cota]

You can always make a few different presets in eq apo and switch them manually based on volume.

 

[gnarly]

I'm not even sure if you can do dynamic EQ with FIR? Most probably, the dynamic EQ is just a minimum phase implementation.

I'm not an expert on dynamic EQs or mutli-band compressors/limiters, but I have played with some on prosound mixers and loudspeaker processors.
Also DIY'ed a few in Q-Sys, like one shown below.

Afaict, they all tend to work by summing some filter with signal in level dependent fashion. So, basically a particular filter being activated by a side chain limiter.
The filter could be anything.....,a collection of IIR PEQ/shelves for example, or FIR filters doing the same same thing, etc.
If the dynamic filter is FIR, the main signal will have to have the same delay as the FIR filter, but otherwise no problem, and little difference in implementation.

Here's a DIY dynamic filter being used for both dynamic PEQ limiting centered around 58Hz, and for implemented a variable order high-pass filter.
Project was a bass reflex sub using the Faital 18FH500, which runs out of xmax well above the low corner.
Since I was going to the trouble of making the dynamic filter, I also added in the variable order high-pass, think I get the benefit of sealed at low SPL, and the safety needed for reflex at high SPL. I imagine this technique is getting applied to more and more active reflex subs. I think RCF is using it.

The green trace is before dynamic kicks in, blue at full SPL capability. Peak voltages were the measured amp output into a dummy load.

Personally, I wouldn't fool with using FIR for any filters used for dynamic limiting of the bottom end.
The shape of the magnitude limiting itself, will most likely dominate the phase and group delay curve. Plus, like you showed, it will take one large FIR filter....that has no complementary offset for reducing pre-ring potential.
Last reason I guess, is I kinda agree with sibergaudio,.... just use a hfp....because who cares about increased group delay below where a speaker stops producing.

And strongly agree with everyone who says fix the chuffing.
@PashkaTLT, I humbly join the crowd who says it ain't a dynamic filter task!

 

[mhardy6647]

Yes, just stuffing the port is a useful idea as well.

'aperiodic damping' as found in the much beloved Dynaco A-25 and some of its kin -- and in other loudspeakers before and after, as well.


A not very good (flash) photo of an A-25 "aperiodic vent" -- yellow fiberglass artisanally stuffed between two bits of plastic 'hardware cloth'.

An old athletic sock (or socks, depending on the size of the port) is a classic modeling tool to prototype aperiodic "ports".

 

[Salt]

'aperiodic damping' as found in the much beloved Dynaco A-25 and some of its kin -- and in other loudspeakers before and after, as well.


A not very good (flash) photo of an A-25 "aperiodic vent" -- yellow fiberglass artisanally stuffed between two bits of plastic 'hardware cloth'.

An old athletic sock (or socks, depending on the size of the port) is a classic modeling tool to prototype aperiodic "ports".

What's that bass/horn/tweeter on the right?