TOPIC:

This ("Sub eq") is listed in the dropdown box where you can select peak or shelf type EQs. I couldn't find much about it in docs/data sheet, other than that it needs two PEQ slots to work. Can anyone fill me in about what this is for? The effect in the shown curve looks just kind of like a peak eq...

thanks,
Bill

"SUB_EQ Create a dip or a peak in the frequency response at low frequencies (10 to 50 Hz). This filter type is similar to PEAK but gives more accurate results for low frequencies. Note that activating any SUB_EQ filter reduces the number of available filters on that channel from ten to nine." (from User Manual)

The background is that a while ago there was a kerfuffle when people tried to use PEQ below 20 Hz and discovered that the results weren't as expected. SUB-EQ was the solution to that.

Also AFAIK it doesn't use two PEQ slots, it reduces the total by one (regardless of how many are used). No idea why.

I've never used it myself.

@ Bill

Good question indeed.. John as usual is right on target. That SUB EQ is actually a carryover from the SigmaDSP days (not as powerful) for Low frequency + High Q + high sample rate (these 3 aren't exactly friends). We had to do a trick based on some biquad papers.

On the Sharc platform, we actually don't need it. We forgot to remove it. We should really remove it and replace it by All Pass filter. What do you guys think?

DevTeam

Yes, all-pass would be a great addition.
Or a direct-entry Linkwitz Transform (that doesn't need calculation out on a spreadsheet)

Great suggestion. Let us go ahead with this.
Flexible Q for the APF? Most phase control "knob" would have a fixed Q.. I'd think that designers would find it useful to be able to tweak the Q of the APF.. just a thought.

DevTeam

Yes, just a generic 2nd order All-Pass would do it, adjust for break frequency and Q. A 1st order AP would be nice, too, but not necessary.

devteam wrote:

@ Bill

Good question indeed.. John as usual is right on target. That SUB EQ is actually a carryover from the SigmaDSP days (not as powerful) for Low frequency + High Q + high sample rate (these 3 aren't exactly friends). We had to do a trick based on some biquad papers.

On the Sharc platform, we actually don't need it. We forgot to remove it. We should really remove it and replace it by All Pass filter. What do you guys think?

DevTeam

Yes APF would be fantastic!

Check out the newest 2x4HD1 for the APF.. maybe doing the trick..

Devteam

It's been 4 years and 9 months since this post was started.  SUB_EQ is still in the drop-down, APF (in PEQ) appears to not be implemented . . .

Am I missing something?

devteam wrote:

@ Bill

Good question indeed.. John as usual is right on target. That SUB EQ is actually a carryover from the SigmaDSP days (not as powerful) for Low frequency + High Q + high sample rate (these 3 aren't exactly friends). We had to do a trick based on some biquad papers.

On the Sharc platform, we actually don't need it. We forgot to remove it. We should really remove it and replace it by All Pass filter. What do you guys think?

DevTeam
 

2022 and the option is still there.

It’s actually replaced with APF 
I would love to see a first order all pass as well

you need to update your firmware to get the change apparently you’re running really old firmware. the APF was implemented years ago 

 

denver8me4dinner wrote:

It’s actually replaced with APF 
I would love to see a first order all pass as well

you need to update your firmware to get the change apparently you’re running really old firmware. the APF was implemented years ago 


 

I'm on the latest firmware for the DDRC-24 (july 2021 - v 1.11 / xmos 1.14). Dropdown options for PEQ are PEAK, LOW_SHELF, HIGH_SHELF and SUB_EQ.

Aah ddrc , yeah with Dirac live adding an allpass could more than likely be detrimental to sound quality, as Dirac will create an allpass that fits the entire spectrum for each channel. 

I would just simply not use subeq and just use peq …. 

post Dirac sound be everything you could ever want