Taking and Interpreting Measurements with REW (FREE eBook)

[john61ct]

Infinite taps? What is this filter? And how long does it take to get to infinety?

I mean, the hypothetical convolver not being limited by hardware processing capacity, in a practical sense. Like preceding the question with "in an ideal world"...

 

[Keith_W]

I mean, the hypothetical convolver not being limited by hardware processing capacity, in a practical sense. Like preceding the question with "in an ideal world"...

Practically ALL PC's are not limited by processing capacity if we are talking about convolution. It's a very low in CPU demand. The only question is: why would you want to? You would suffer so much latency that you may as well watch grass grow.

 

[SigbergAudio]

Damn it, trust you guys to drag the thread off topic with a discussion about smoke alarms! At least it's not about cars!

It was an attempt at being at least mostly on topic, pointing out that 75dB isn't universal in every country, so potentially a bad suggestion for how to calibrate. If I used mine, I'd get something like 95dB.

 

[Keith_W]

It was an attempt at being at least mostly on topic, pointing out that 75dB isn't universal in every country, so potentially a bad suggestion for how to calibrate. If I used mine, I'd get something like 95dB.

That's fair. It's 75dB in Australia.

 

[john61ct]

Practically ALL PC's are not limited by processing capacity if we are talking about convolution. It's a very low in CPU demand. The only question is: why would you want to? You would suffer so much latency that you may as well watch grass grow.

Yes I so far haven't cared a wit about latency, even minutes' delay, so long as the main LP arrival time is in sync across all channels and frequencies.

I am puzzled why anyone would, in a recreational music listening context?

I am not producing / mixing music.

My video player has tunable delay if I notice lip syncing issues.

I do not game.

Doesn't all that mean latency is a non-issue?

 

[john61ct]

if we are talking about convolution

Linear phase crossovers, really ANY processing of delays / timing / phase alignment tuning

requires FIR, is that not so?

Any chance you (or anyone) could help my understanding of this issue?

Should I just do all my crossovers from scratch as linear phase? No advantages to doing IIR or other lesser phase-aware filter types, other than resource-constrained convolvers?

 

[Grimoire]

Yes I so far haven't cared a wit about latency, even minutes' delay, so long as the main LP arrival time is in sync across all channels and frequencies.

I am puzzled why anyone would, in a recreational music listening context?

I am not producing / mixing music.

My video player has tunable delay if I notice lip syncing issues.

I do not game.

Doesn't all that mean latency is a non-issue?

So minutes of delay of the audio is acceptable when watching TV? What a strange world you must live in.

 

[Keith_W]

Doesn't all that mean latency is a non-issue?

Latency makes my system feel sluggish and slow to respond. Want to change the track - wait a couple of seconds. Want to change the volume - wait a couple of seconds. When people come over to listen, I have to warn them that there is input lag in my volume control. Otherwise they change the volume, hear nothing, change the volume again, and then the system will blast them with sound. I am used to that volume control, so it doesn't bother me. But it's annoying when I want to change tracks.

Linear phase crossovers, really ANY processing of delays / timing / phase alignment tuning
requires FIR, is that not so?
Any chance you (or anyone) could help my understanding of this issue?

Well you COULD have linear phase IIR's using subtractive delays, but AFAIK there is no easy way to implement it. You would need something like Audio Weaver to design such a filter. May as well stick with FIR, it's easier to design. To understand how FIR and IIR works, take a look at this thread.

 

[john61ct]

So minutes of delay of the audio is acceptable when watching TV?

No house I've lived in has had anything like "TV" since I was a child. I've also never paid for "cable" Do those even exist anymore like they did last millenium?

Furthermore, we've never had any media streaming service subscriptions, and the only discs were ones I burned myself, for my kids to watch, also long ago. The occasional film these days is from downloaded files only, same with show binges, long after they've stopped making it.

So yes, maybe that makes me strange? But no, the purpose of my audio systems is 96% music only.

 

[john61ct]

Latency makes my system feel sluggish and slow to respond. Want to change the track - wait a couple of seconds. Want to change the volume - wait a couple of seconds.

That seems like a lot, but I guess I'll see while testing.

In any case, my main question still stands, I was just saying "ignore latency" as part of the context, I suspect your answer is actually still focused on that.

Here is the OG question, with no concern about # of taps (nor latency)

Should I just do all my crossovers from scratch as linear phase? No advantages to doing IIR or other lesser phase-aware filter types, other than resource-constrained convolvers?

As opposed to using the FIR for delays / timing / alignment tuning, e.g. to correct / "unwrap" the phase issues of existing non-FIR (or even non-DSP) crossovers


And again, constructive answers are welcome, from anyone.

I believe this one also still stands?


> Linear phase crossovers, really ANY processing of time or phase domain requires FIR, is that not so?

 

[Keith_W]

If you have FIR, you can make linear-phase filters and minimum-phase filters and compare them at the push of a button. FIR is a very powerful tool. But remember: the more powerful the tool, the more dramatically you can screw it up. So ... SHOULD you? I don't know, that's a question that only you can answer.

If you have IIR, linear-phase is out of the question unless you are very smart. We are talking Charlie Laub or Greg Berchin level of "smart" here.

 

[john61ct]

OK, that is helpful.

But my question is not so much about a choice between from-scratch FIR crossovers, and from-scratch "minimum phase" filters

but between using from-scratch DSP crossovers as opposed to using DSP to "correct" existing non-DSP crossovers assuming their magnitudes look just fine but REW shows phase issues, or that delays are needed for time-of-arrival.

 

[SigbergAudio]

> Linear phase crossovers, really ANY processing of time or phase domain requires FIR, is that not so?

Not sure if I am answering somewhat out of context here, but 1.order crossover filters (IIR) will be linear phase.

 

[Keith_W]

Not sure if I am answering somewhat out of context here, but 1.order crossover filters (IIR) will be linear phase.

I think it is necessary to explain what you said a bit further to avoid confusing the newbies. I know that you know this, but others may not. So:

A first order HPF or LPF are MINIMUM-PHASE, not linear phase. They rotate phase by 90deg for every order.

Here is a first order Butterworth LPF/HPF with a corner frequency of 100Hz. Above: amplitude, below: phase. We can see the expected minimum-phase behaviour: total phase rotation of 90deg, with half the phase rotation (45deg) at the corner frequency of 100Hz. But when we sum them:

The result is linear phase / constant group delay across the passband.

However, because the filter still remains causal, it lacks other characteristics of linear phase FIR filters.

 

[EJ3]

No house I've lived in has had anything like "TV" since I was a child. I've also never paid for "cable" Do those even exist anymore like they did last millenium.

Furthermore, we've never had any media streaming service subscriptions, and the only discs were ones I burned myself, for my kids to watch., also long ago. The occasional film these days is from downloaded files only, same with show binges, long after they've stopped making it.

So yes, maybe that makes me strange? But no the purpose of my audio systems is 96% music only.

My wife asked me in 2007: "Do we need to have this (meaning this or any other) TV"? I said: "No, not really." She said, "I'll get rid of it, then." I said "Fine." We haven't had a TV since then.

 

[Keith_W]

Hello all, I have updated both books 1 and 2. Both books are available in the original link. Here it is again: LINK.

What's new:

Book 1: more thorough explanation of why rooms affect the bass frequency response. Added a new section on how to compare measurements (I kept this section out of the main eBook).

Book 2: added acoustic targets to each measurement and some small errata fixed. Expanded remarks on a few of the more acoustic common measurements.

There are a couple of new documents in the folder:

MAC Talk Treble. These are slides from the talk I gave at the Melbourne Audio Club on 15 Jul 26 pertaining to the acoustics of frequencies above Schroder, how to measure them, as well as a basic discussion on the roles of speaker positioning and room treatment.

Mac Talk Bass. This will be made available after I give that talk, which will be in September.

Acoustic Targets for Listening Rooms by Nyal Mellor. I did not write this document, I found it on another webpage. All these targets have been published elsewhere, but here it has been nicely compiled for your convenience.

 

[MaxwellsEq]

Hello all, I have updated both books 1 and 2. Both books are available in the original link. Here it is again: LINK.

What's new:

Book 1: more thorough explanation of why rooms affect the bass frequency response. Added a new section on how to compare measurements (I kept this section out of the main eBook).

Book 2: added acoustic targets to each measurement and some small errata fixed. Expanded remarks on a few of the more acoustic common measurements.

There are a couple of new documents in the folder:

MAC Talk Treble. These are slides from the talk I gave at the Melbourne Audio Club on 15 Jul 26 pertaining to the acoustics of frequencies above Schroder, how to measure them, as well as a basic discussion on the roles of speaker positioning and room treatment.

Mac Talk Bass. This will be made available after I give that talk, which will be in September.

Acoustic Targets for Listening Rooms by Nyal Mellor. I did not write this document, I found it on another webpage. All these targets have been published elsewhere, but here it has been nicely compiled for your convenience.

Thank you!

 

[Holmz]

Hello all, I have updated both books 1 and 2. Both books are available in the original link. Here it is again: LINK.

What's new:

Book 1: more thorough explanation of why rooms affect the bass frequency response. Added a new section on how to compare measurements (I kept this section out of the main eBook).

Book 2: added acoustic targets to each measurement and some small errata fixed. Expanded remarks on a few of the more acoustic common measurements.

There are a couple of new documents in the folder:

MAC Talk Treble. These are slides from the talk I gave at the Melbourne Audio Club on 15 Jul 26 pertaining to the acoustics of frequencies above Schroder, how to measure them, as well as a basic discussion on the roles of speaker positioning and room treatment.

Mac Talk Bass. This will be made available after I give that talk, which will be in September.

Acoustic Targets for Listening Rooms by Nyal Mellor. I did not write this document, I found it on another webpage. All these targets have been published elsewhere, but here it has been nicely compiled for your convenience.

When in September?
(A treo of us are heading to a concert on grand final weekend.)

 

[john61ct]

grand finale of what?

 

[Keith_W]

When in September?
(A treo of us are heading to a concert on grand final weekend.)

16th September, in the Willis Room in the Whitehorse City Council Building, in Nunawading.

@john61ct he is referring to the Australian Football League (AFL) Grand Final, on the 26th of September.

BTW the "advanced" eBook now has a section on how to diagnose problems in the bass response, on page 40. Since writing it I have realized it's a bit too short (leaves too much stuff out), but if I wanted to properly explain it I would need a greatly longer section. So that means I need to restart my subwoofer integration guide, which has been put on hold for a few months now.