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Eclipse Audio FIR Designer

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Michael John:

--- Quote from: Mark Wilkinson on December 09, 2021, 12:12:51 PM ---.... If you are using an average of a few angles generate the FIR correction, I'm not exactly sure how FirDesigner's various averaging options handle phase..over my pay grade still.
I've been using Smaart's Averager with default settings, because it makes for a little easier workflow.

If the measurements are simply for displaying polars, where you want to show phase too, I usually reset delay finder for each meas.

--- End quote ---

Great thread. Mark, thanks for the shout outs.

Sorry I'm lake to the party. :-) I thought I'd throw in some comments re FIR Designer's averaging.

When loading measurements on the "Load and Setup" tab, one measurement can be noted as the "reference" - e.g. the on-axis measurement. The notion of "reference" is used by the following features.

"Move Ref IR Peak to 0" automatically removes any time delay from the "reference" measurement, bringing its IR peak sample to 0 time.  (This is similar to SMAART's "Delay Finder" for TF measurements.) The same delay adjustment is also applied to all other measurements and so the relative time delay, between measurements, is retained. This is useful for complex averaging of turntable measurements of individual drivers in a multi-way, with one caveat. Assuming the time delay - in the measurement system - is locked for all measurements across all multi-way drivers, to maintain relative delay between drivers use "Move Ref IR Peak to 0" for, say, the HF average, then manually apply this delay in the "Apply common delay (ms)" field when averaging measurements for each of the other drivers.

"Time Align all to Reference" automatically adjusts the delay of all other measurements to match the reference and so lines up the IR peaks. Relative time delay or phase between measurements is discarded but cabinet phase characteristics are retained. This is useful when complex, spatially averaging full BW measurements of a loudspeaker to do mag & phase adjustment of the whole cabinet.

BTW on the "Average" tab, there're tools to quickly check each measurement, remove bad measurements by unchecking "Use" and manually tweak time delay.

To ensure no individual measurement dominates the averaging, on the "Load and Setup" tab use the "Normalise magnitudes to max" or "Normalise to frequency range" options.

Re the actual averaging modes

* Complex: This is full transfer function averaging. The phase of the cabinet is retained.
* Power (flat, zero phase): This power averages the magnitude only and discards the phase.
* Power (minimum phase): This power averages the magnitude only and discards the phase, then calculates the minimum phase response from the magnitude response. For a single driver in an anechoic chamber, the resulting phase should be very similar to the full Complex average. For a multi-way system with crossovers, this mode gives the cabinet phase response minus the additional or "excess" phase from crossovers.
* Power (complex phase): This power averages the magnitude only then combines this mag with the phase from the Complex averaging mode.
* Power (min. phase + Ref. excess phase): This is the same as the "Power (minimum phase)" mode but the excess phase from the Reference measurement is added in. (The Reference excess phase is the original phase minus the phase from a minimum-phase calculation from the Reference magnitude.) In a nutshell it's calculating the excess or crossover related phase from the Reference measurement, then adding this crossover phase to a minimum-phase average of all the measurements.
* Power (with complex avg. excess phase): The magnitude is a power average and the phase is the excess phase only. This could be useful for isolating excess or crossover related phase and only correcting this phase. We're not aware of anyone using this but it was easy to calculate so we thought it worth including.
Cheers,
Michael

Michael John:

--- Quote from: Helge A Bentsen on January 24, 2022, 03:16:33 AM ---Another thing that surfaced here.

I've tried a few things, and to my ears it seems like using IIR filters to adjust the response of each frequency band sounds better than using auto mag, even if the result looks similar in supplementary responses. My best sounding preset to date is done using IIR to correct as much as possible before I apply a LF/HF linear phase crossover, a couple of manual linear phase eq to adjust summation and a couple of manual filters to adjust the phase response as needed.
I then apply a tiny bit of auto mag/phase to the HF, leaving the LF manually adjusted.


Does this sound familiar to others using FIR Designer?
I still have a couple of things I need to work out, there is a bit of "jumpyness" in the horn, some part of the spectrum stick out a bit on some recordings. I suspect I might have overcorrected a bit on the HF, going to do a A/B with a version without auto mag correction.
BTW that is an advantage of sticking to IIR filters, it's really easy to fine-tune a filter directly in the DSP, no need to load a new FIR filter on the outputs.

--- End quote ---

That all makes sense. Just to add to Mark's reply, the "Oct Smooth" setting in the Auto Mag makes a difference. If it's too fine - say 1/24th oct or 1/48th oct - it could over-push some narrow notches, which might be what you are experiencing. I've personally never used finer than 1/6th oct unless I've first averaged a lot of measurements.

We are looking at updates to the Auto Mag process to provide some independent control of pushes versus cuts.

BTW re using IIR's only, I recently tuned FOH in a church install that had a QSC PLD - no FIR. I took about 20 measurements in the room with SMAART, averaged in FIR Designer, then on the FIR Designer IIR tab, selected the QSC IIR mode, placed a few filters to push the measurement to target and manually copied the IIR settings into the PLD. Overall really quick and the result was excellent, despite the limited number of IIR's in the PLD.

Mark Wilkinson:

--- Quote from: Michael John on January 30, 2022, 12:19:04 AM ---
Re the actual averaging modes

* Complex: This is full transfer function averaging. The phase of the cabinet is retained.
* Power (flat, zero phase): This power averages the magnitude only and discards the phase.
* Power (minimum phase): This power averages the magnitude only and discards the phase, then calculates the minimum phase response from the magnitude response. For a single driver in an anechoic chamber, the resulting phase should be very similar to the full Complex average. For a multi-way system with crossovers, this mode gives the cabinet phase response minus the additional or "excess" phase from crossovers.
* Power (complex phase): This power averages the magnitude only then combines this mag with the phase from the Complex averaging mode.
* Power (min. phase + Ref. excess phase): This is the same as the "Power (minimum phase)" mode but the excess phase from the Reference measurement is added in. (The Reference excess phase is the original phase minus the phase from a minimum-phase calculation from the Reference magnitude.) In a nutshell it's calculating the excess or crossover related phase from the Reference measurement, then adding this crossover phase to a minimum-phase average of all the measurements.
* Power (with complex avg. excess phase): The magnitude is a power average and the phase is the excess phase only. This could be useful for isolating excess or crossover related phase and only correcting this phase. We're not aware of anyone using this but it was easy to calculate so we thought it worth including.
Cheers,
Michael

--- End quote ---

Thank you Michael,
like i said earlier, understanding how FirD handles phase and averaging is above my pay grade....and still is until i digest all you wrote here!   :)

Oh, and +1 to using less fine corrections in Auto Mag, as you mention in next post.  I should have brought that up previously.
1/6th has become my go-to, sometimes less..... with 1/12th tops for super well behaved drivers.
I've slowly weened off trying to get near perfect measurements!  lol

Helge A Bentsen:

--- Quote from: Michael John on January 30, 2022, 12:19:04 AM ---Great thread. Mark, thanks for the shout outs.

Sorry I'm lake to the party. :-) I thought I'd throw in some comments re FIR Designer's averaging.

When loading measurements on the "Load and Setup" tab, one measurement can be noted as the "reference" - e.g. the on-axis measurement. The notion of "reference" is used by the following features.

"Move Ref IR Peak to 0" automatically removes any time delay from the "reference" measurement, bringing its IR peak sample to 0 time.  (This is similar to SMAART's "Delay Finder" for TF measurements.) The same delay adjustment is also applied to all other measurements and so the relative time delay, between measurements, is retained. This is useful for complex averaging of turntable measurements of individual drivers in a multi-way, with one caveat. Assuming the time delay - in the measurement system - is locked for all measurements across all multi-way drivers, to maintain relative delay between drivers use "Move Ref IR Peak to 0" for, say, the HF average, then manually apply this delay in the "Apply common delay (ms)" field when averaging measurements for each of the other drivers.

"Time Align all to Reference" automatically adjusts the delay of all other measurements to match the reference and so lines up the IR peaks. Relative time delay or phase between measurements is discarded but cabinet phase characteristics are retained. This is useful when complex, spatially averaging full BW measurements of a loudspeaker to do mag & phase adjustment of the whole cabinet.

BTW on the "Average" tab, there're tools to quickly check each measurement, remove bad measurements by unchecking "Use" and manually tweak time delay.

To ensure no individual measurement dominates the averaging, on the "Load and Setup" tab use the "Normalise magnitudes to max" or "Normalise to frequency range" options.

Re the actual averaging modes

* Complex: This is full transfer function averaging. The phase of the cabinet is retained.
* Power (flat, zero phase): This power averages the magnitude only and discards the phase.
* Power (minimum phase): This power averages the magnitude only and discards the phase, then calculates the minimum phase response from the magnitude response. For a single driver in an anechoic chamber, the resulting phase should be very similar to the full Complex average. For a multi-way system with crossovers, this mode gives the cabinet phase response minus the additional or "excess" phase from crossovers.
* Power (complex phase): This power averages the magnitude only then combines this mag with the phase from the Complex averaging mode.
* Power (min. phase + Ref. excess phase): This is the same as the "Power (minimum phase)" mode but the excess phase from the Reference measurement is added in. (The Reference excess phase is the original phase minus the phase from a minimum-phase calculation from the Reference magnitude.) In a nutshell it's calculating the excess or crossover related phase from the Reference measurement, then adding this crossover phase to a minimum-phase average of all the measurements.
* Power (with complex avg. excess phase): The magnitude is a power average and the phase is the excess phase only. This could be useful for isolating excess or crossover related phase and only correcting this phase. We're not aware of anyone using this but it was easy to calculate so we thought it worth including.
Cheers,
Michael

--- End quote ---

Just to follow up on this, when you do turntable measurements of a speaker, what do you consider best practice?

Since I'm measuring indoors ATM (weather issues) I got the best resuls with this method:
- Measure delay differences between various pass bands and apply delay/level adjustments first in the DSP. All bands delay adjusted in the processor so they all end up with the same delay time in Smaart using the delay finder. Level set so all bands are roughy equal in level.
- Measure each pass band individually, from 0 to X degrees off-axis.

Secondly, how should one proceed to average each passbands measurements together? Time align to reference + normalise to max?
I noticed that if I used "Time align to refererence" the impulse response of the averaging got sharper compared to Smaarts averager.
And if I normalised to max the level of the average got higher, so the level in FIR D more resembled the on-axis response of the speaker.
This was helpful because in my first tuning I ended up with too much level on the horn on-axis, this was easier to get right when I normalised before averaging.

Michael John:
Hi Helge,

I think your measurement setup makes sense. You could leave out the initial delay and level adjustments, and just set SMAART delay finder using an on-axis measurement of the deepest driver - usually the horn. Then delay and level adjustments can be done in FIR Designer M as part of the overall preset design, after averaging.

Regarding averaging, I tend to not time align all the measurements to the reference, and then I do a complex averaging for each driver, but I generally work within modest coverage angles (+-45 degrees). It's worked for me in the past but might not work as well for wider angles. Re normalisation, I usually apply a common gain to all measurements across all drivers, so that the bulk level differences between drivers are maintained for FIR Designer's "Gain/Polarity/Delay" tab.

(For horn reflection correction, I'd suggest time aligning all to reference and then doing a complex average. This averaging should tend towards isolating complex, angle-invariant aspects of the horn.)

I think Mark's approach with SMAART - if delay finder is adjusted for each measurement - is analogous to time aligning all to the reference in averaging.

I'd recommend taking a look at FIR Designer M's "supplementary responses." Here sets of measurements for each driver can be loaded, matched and plotted with all gain/polarity/delay/IIR/FIR processing applied. The combined response, across all drivers, is also shown. With this feature you can work on the tuning with on-axis driver measurements, and simultaneously view the processed, combined response for many off-axis directions.

Related this, I'm working on another tool that shows polar and balloon plots of the acoustic sum of the driver measurements with processing applied. With this it's possible to see how the processing/crossover works across many angles and check the average of the combined acoustic response (with processing). I can't say when it will be ready.

Best,
Michael

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