Pre and post ringing in amplitude and phase corrections

[QMuse]

Do you think this could be tested?

I have the amps and sutiable speakers, a UMK1, & REW, but I'm not prepared to move the speakers, would a nearfiled in room measurment show anything?

Yes, REW measurement should show phase correctly. Try making a sweep measurement from app 70cm away from the speaker, use "Estimate IR delay" and shift IR for as much as REW suggests and then apply FDW of 5 cycles. With a little luck wou will get a clean phase response graph.

 

[JohnYang1997]

Ok, to make things clearer let's assume we are speaking about a speaker with a single wideband driver. How do you correct phase without introducing pre-ringing?

Because the magnitude and phase are bound due to minimum phase nature of single driver. You just use minimum phase filter to correct the magnitude response then you will have phase corrected automatically.

 

[JohnYang1997]

I don't really understand what's being discussed here.

Prering in non-minimum phase filter means it delays the lower frequency to compensate for the already occurred phase delay in the high frequency.

Minimum phase system or filter always can be reversed using minimum phase filter meaning headphones, single driver speakers can be corrected using minimum phase filter solely.

Is there any issue here?

 

[Soniclife]

You should be able to measure the phase response of the woofer with a nearfield (or near-ish field) measurement and then compare it to the same measurement with the SAM system engaged. If the crossover phase distortion is being corrected, you'd expect to see a flatter phase response towards the top of the woofer's passband.

Perhaps @KSTR, who is really the expert on these matters, has a better idea of the best way to measure this in-room?

Assuming an ideal case for e.g. a midwoofer in a sealed box with an F3 of 40Hz crossed over to a tweeter at 2kHz/LR4, you'd expect to see something like this (red = uncorrected, blue = corrected):

View attachment 51798

I'd be very interested to know what you find...

I'll give it a go when I have time.
BTW Sam only works up to 150hz, so it's about the bottom end only, I would not expect to see any change up at the crossover point.

 

[Pio2001]

That's exactly my original point (assuming the question was rhetorical )

You can't. This is what imo Devialet seems to claim to be doing, and the basis of my scepticism.

What you can do with a multiway (without introducing on-axis pre-ringing) is to correct phase distortion resulting from the crossover, so that the whole system has minimum-phase behaviour. This is KSTR's point, and I assume what the Devialet might actually be doing.

The correction is only valid on the design axis though, so there will be pre-ringing off-axis, especially pronounced for non-coaxials.

And as mentioned, the bass roll-off will remain minimum (not linear) phase.

Sorry, I don't understand.
You say that it is impossible to correct phase without introducing pre-ringing, then you say that it is possible without introducing on-axis pre-ringing.

Introducing pre-ringing is not related to a physical speaker nor to the convolution engine kernel, it is purely a mathematical model thing - as soon as you define a single phase correction filter within minimum-phase high-pass filtered amplitude response you will get a pre-ringing and there is no escaping from this.

What do call a "single phase correction filter within minimum-phase high-pass filtered amplitude response" ???

Too many words in one sentence !

 

[KSTR]

Introducing pre-ringing is not related to a physical speaker nor to the convolution engine kernel, it is purely a mathematical model thing - as soon as you define a single phase correction filter within minimum-phase high-pass filtered amplitude response you will get a pre-ringing and there is no escaping from this.

I don't fully understand your second paragraph...

Anyway, the basic situation is like this: Only a mininum-phase system is free of pre-ringing by design and definition, but of course has post-ringing. The natural roll-offs of the system under test is a typical example, but any non flat frequency response also produces post-ringing in the time domain, look for example at a notch filter.

Introducing anything in the system which has allpass behavior (flat FR, varying phase only) will produce ringing. Either post-ringing only (for example typical system allpass from a regular crossover), or any mix of post- and pre-ringing.

Introducing anything in the system which has magnitude-only behavior (flat phase, varying FR only) will also produce (pre-)ringing of any flavor. An example is linear-phase general purpose equalizers which have found little use in audio.

For speakers, this means the target response must be minimum-phase, for example no correction of the phase, time-lag and ringing of 6th-order system highpass (4th order ported + 2nd order subsonic filter). One can do so, partly at least, but has to be aware that it is a compromise. You can "speed up the bass" but you may notice the occasional pulse-widening and pre-ringing effect with specific signals. It's a trade-off between 'pulse position precision' and 'pulse shape/length precision', pulse meaning short bass transients.

A second-order theme is the one I discussed as well when off-axis cancellations don't fully work.

Very occasionally we need linear-phase filters and system targets (or at least not fully min-phase) but normally the strategy is: use minimum-phase correction for minimum phase-problems.

 

[Soniclife]

You should be able to measure the phase response of the woofer with a nearfield (or near-ish field) measurement and then compare it to the same measurement with the SAM system engaged. If the crossover phase distortion is being corrected, you'd expect to see a flatter phase response towards the top of the woofer's passband.

Yes, REW measurement should show phase correctly. Try making a sweep measurement from app 70cm away from the speaker, use "Estimate IR delay" and shift IR for as much as REW suggests and then apply FDW of 5 cycles. With a little luck wou will get a clean phase response graph.

I've had a go, there are 2 sets of measurements, one from very close to the woofer, and one from about 70cm. They don't tell me much.

 

[QMuse]

I've had a go, there are 2 sets of measurements, one from very close to the woofer, and one from about 70cm. They don't tell me much.

And now?

From your 70cm measurement:

 

[Soniclife]

And now?

Still not much. I can see they change, but I don't understand this stuff enough.

 

[QMuse]

Still not much. I can see they change, but I don't understand this stuff enough.

Hmm.. I'm also not sure what to think of it. Let's wait for the comments from @KSTR and @andreasmaaan .

 

[BYRTT]

If you ask me for SAM off verse the others SAM enabled the difference is they linearize excess phase of XO point where woofer hand over to mid and omit linearize where mid handover to tweeter, a politic as that makes sense IIRC XO points are @500Hz @3000Hz, because our hearing have it hard detect phase turn as frequency goes up say above 1-2kHz and also because most speakers have a natural stopband at 20kHz area that bandwith limit hinder correct timing to reproduce of squarewave so above say 6kHz area a reproduced squarewave will distort and be impossible.

 

[Soniclife]

If you ask me for SAM off verse the others SAM enabled the difference is they linearize excess phase of XO point where woofer hand over to mid and omit linearize where mid handover to tweeter, a politic as that makes sense IIRC XO points are @500Hz @3000Hz, because our hearing have it hard detect phase turn as frequency goes up say above 1-2kHz and also because most speakers have a natural stopband at 20kHz area that bandwith limit hinder correct timing to reproduce of squarewave so above say 6kHz area a reproduced squarewave will distort and be impossible.

Mine are 2 way speakers.

 

[QMuse]

If you ask me for SAM off verse the others SAM enabled the difference is they linearize excess phase of XO point where woofer hand over to mid and omit linearize where mid handover to tweeter, a politic as that makes sense IIRC XO points are @500Hz @3000Hz, because our hearing have it hard detect phase turn as frequency goes up say above 1-2kHz and also because most speakers have a natural stopband at 20kHz area that bandwith limit hinder correct timing to reproduce of squarewave so above say 6kHz area a reproduced squarewave will distort and be impossible.

Have a look at the excess phase graphs of SAM Off vs SAM 100%:

SAM Off:

SAM 100%:

Phase overlay:

 

[Soniclife]

Have a look at the excess phase graphs of SAM Off vs SAM 100%:

SAM Off:

View attachment 53201


SAM 100%:

View attachment 53202

Phase overlay:

View attachment 53203

This is what confuses me, it looks worse with it on in an area they claim to fix.

 

[QMuse]

This is what confuses me, it looks worse with it on in an area they claim to fix.

Excess phase certainly apperas to look worse, but let's wait for the expert's opinion.

GD:

 

[BYRTT]

Mine are 2 way speakers.

Okay sorry thought it was 8341A that amirm anounced have 500/3000Hx XO points, do you have numbers as @frq and order of slope from manual.

Have a look at the excess phase graphs of SAM Off vs SAM 100%:.....

Year differences look they linearize phase for a allpass/excess minimum phase away of some natural summing XO point, rest of the phase turn in lows is the natural AC like coupled roll off stopband that probably is huge if X scale is set to look below 20Hz and typycal its a 6-8th order number for active ported systems and being a 90deg shift per order then out of band numbers at lows can be up to a huge +720deg.

 

[QMuse]

Btw, all these graphs were generated with FDW of 4 applied.

 

[QMuse]

Year differences look they linearize phase for a allpass/excess minimum phase away of some natural summing XO point, rest of the phase turn in lows is the natural AC like coupled roll off stopband that probably is huge if X scale is set to look below 20Hz and typycal its a 6-8th order number for active ported systems and being a 90deg shift per order then out of band numbers at lows can be up to a huge +720deg.

I have no clue about what you just said, but it certainly looks like you know what you're talking about.

 

[Soniclife]

Okay sorry thought it was 8341A that amirm anounced have 500/3000Hx XO points, do you have numbers as @frq and order of slope from manual.

This is Devialet SAM, not genelec SAM, different thing, the speakers are Sonus Faber Guarneri Evolutions, driven by Devialet 440pro.

What's claimed...
https://www.devialet.com/en-gb/expert-pro-sam-ready-speakers/sonus-faber/guarneri-evolution/

3rd party speaker measurements.
https://www.stereophile.com/content/sonus-faber-guarneri-evolution-loudspeaker-measurements

 

[BYRTT]

Still not much. I can see they change, but I don't understand this stuff enough.

This is Devialet SAM, not genelec SAM, different thing, the speakers are Sonus Faber Guarneri Evolutions, driven by Devialet 440pro.

What's claimed...
https://www.devialet.com/en-gb/expert-pro-sam-ready-speakers/sonus-faber/guarneri-evolution/

3rd party speaker measurements.
https://www.stereophile.com/content/sonus-faber-guarneri-evolution-loudspeaker-measurements

Thanks links for products and sorry i thought it was Genelec 8341A, lets see if we analyze phase stuff for your speaker based on stereophile measurements that it will help understand phase stuff better. In below curves that is traced from over stereophile site i see one error that is system roll off in lows is somehere beteen 2nd and 3rd order slope and that is not in line with a ported tuning will be of 4th order roll off so think for system sum curve they had some room gain into their measured curve, but nevermind we live with error here its just than phase turn in positive direction (delay) in lows should had been close to double so much and also amplitude roll off slope should had been steeper.

Imagine you okay read and understand amplitude curves that below black is system sum of your speaker and its a parallel sum of woofers blue curve plus tweeters red curve. Now it so that was it possible transducers could reproduce frequency cycles from 0Hz (DC) to infinite high frequency (lightspeed) then black curve would be flat as pancake in below audioband and so would phase in they related, that relation is in rough numbers that whenever amplitude roll off per one order phase turn is 90deg if we include view or axis scale to look into out of band area.

Green phase curve is how minimum phase will look for amplitude response in black curves system sum, its relative flat and smooth and go in positive direction (delay) in lows (+90deg per order off roll off) and at highs phase goes a bit in minus direction because HF amplitude will roll off outside scale view of X-axis.

Grey phase curve is the real phase curve of this speaker system because remember black curve is not using one single driver with all that nice bandwidth but its a sum of a woofer pluse tweeter that had their stopband roll off a 4th order (4x 90=360deg). That exstra phaseturn from XO point is sometimes called allpass filter or excess phase (differense between green and grey curve).

In relation to topic for this thread one can in DSP linearize above grey curve excess phase relative to green phase curve that belong to amplitude of system. My first thought would be that is what that SAM process is for but weird enough it looks add tons of more phaseshift and while i can imagine it to be audioable i cant imagine it be natural.