Auto EQ for delay or measurement?

[Mr Incredible]

Obviously prior to the introduction of auto EQ on amplifiers, the way to set the delay was to measure the distance from the speakers to the sitting position.

I often see people (and I include myself here) who run auto EQ and then manually measure and manually set the delay (distance) in the amp.

Since many amps are precision bits of kit and will do EQ automatically, why would anyone use a tape measure?

[Piers]

Because, with a few exceptions, the auto EQ routines aren't accurate? The early ones were dire, the latest expensive ones are getting good but with the right tools and experience they can be bettered with manual calibration.

[Neil Davidson]

Piers is being too generous! The equipment we have allows the delay of the entire signal path to be determined and it is amazing how much delay can be added by the in built signal processing.

Getting the delays correct is vital to avoid the comb filtering effect.

Neil

[Mr Incredible]

I was making reference to using a tape measure as opposed to auto EQ. I cannot see how a tape measure can measure the delay of an entire signal path! Unless you open up your kit and measure the circuits?

Seriously though, if small and inconsistent delays are introduced in say the entire "supply chain", say in different crossovers in different speakers, inductance in cables etc, I cannot see how an external physical measure can even attempt to compensate and get the delays correct.

At least with auto EQ the amp has its reference point (generator time point = 0) and the final point, measured SPL from each end of the supply chain (time = time point 0 + supply chain delay).

AV expert I am not, but from an empirical standpoint, tape measures are a poor instrument compared to circuits which will work consistently every time.

Auto EQ processing will use the same "logic" to calculate the delay on each and every channel, and any difference between the measured delays on the channels will be due to a combination of physical position of the speakers AND any delay introduced in the supply chain.

AFAIK delay is about ensuring that all sounds reach the listener at the same time from all the speakers. That delays introduced to compensate for different speaker placements is more to do with the "relative" positions of the speakers, and not with their absolute positions. EQ measures relative, tape measures measure absolute.

As long as the "relative" distances (delays) are correct then I believe it would not make any difference if the amp calculated positions of FL,C,FR,SR,SL, SW or whether it calculated positions of FL+10m, C+10m, FR+10m etc. If any "inaccuracies" in the amp are there then at least they will be applied equally to all channels.

The fact that the amp EQ may "measure" the distance say 300mm different to the physical "measured" location is IMO irrelevant if the 300mm difference is applied on all the channels.

If the amp then measures another channel as having a difference of 200mm to the measured physical location, then I contest that the amp has only picked up added delay differences in the supply chain. IMO it is not a sign that the amp auto EQ has produced an invalid measurement.

Just my $0.02!

[Neil Davidson]

Malice,

The theory in your posting can't be faulted - sadly it is the accuracy of the set up routines that is still at fault.

Setting delays should be one of the single easiest things for a receiver to do correctly but I seriously have not yet encountered one that does it perfectly. When you measure the delay in AV Receivers it as common as not, to find that the procesing is adding delay not accounted for in the auto setup. 18ms error for the fronts on the Pioneer I have. For the clarification of doubt that equates to 18 feet for sound moving through the air!

The problem can often be traced to the fact that the test tones are injected in to the output path after the input processing stage, thus input processing delays are completely ignored. It is for this reason that setting levels with an external tone should always be the prefered option.

HTH

Neil

[Mr Incredible]

Interesting! Thanks.

I can understand it if the auto set up bypasses all processing as part of the set up. In my Denon I notice that the auto set up result, as far as EQ is concerned, suggests that signal processing (small/large crossover) is applied to the test tones because when I have the fronts set to large with a 40Hz crossover, I appear to get EQ adjustments below 40Hz. Put the speakers back to small and 60Hz crossover, and all the "lower" frequencies disappear from the EQ summary for the fronts.

Unless of course my logic is too generous and the amp's EQ will retrospectively adjust the EQ frequencies based on the crossover settings and not measured from the actual test tone frequencies generated through the signal processing?

My brain hurts!

EDIT: On your point about your amp adding 18ms to the fronts; did at add similar or different delays on your centre and rears?

[Neil Davidson]

Originally Posted by Malice

EDIT: On your point about your amp adding 18ms to the fronts; did at add similar or different delays on your centre and rears?

Different, much different!

[Mr Incredible]

OK, I am intrigued as to what kit you use to generate a test tone and measure the delay of all the parts of the processing signal path. How do you hook it up to the AV amp?

[Neil Davidson]

Here is a link to the kit I use:

http://www.sencore.com/products/audiosuite.htm

As you will see, this allows me to hook up to any input on the Receiver/Processor and supply accurate tones.

Neil

[russ.will]

Been following this thread with interest.

Neil, I notice that in the 'Radioshack SPL meter' thread, with respect to YPAO, you mention it being no better than "all the other non Audyssey auto setups".

In the light of the above posts, what makes Audyssey better than the rest?

And while I'm in full blooded hijack mode (sorry Malice), where a bass EQ device is in use, I presume it is correct to EQ the bass with positional fine tuning of speakers, then EQ and then run the Auto EQ?

When EQing, I take great care over phase adjustment to smooth the response prior to messing with filters, but then the Auto EQ jumps in an adds a dose of added distance to account for the EQ processor delays, amongst others.

But as distance and phase are closely related, I seem to end up chasing my own tail, setting one then running the other only to start again. Any words of wisdom?

Cheers

Russell

[Mr Incredible]

Originally Posted by ceenhad

Here is a link to the kit I use:

http://www.sencore.com/products/audiosuite.htm

As you will see, this allows me to hook up to any input on the Receiver/Processor and supply accurate tones.

Neil

The SoundPro Audio Analyzer weighs in at about $2,000.
Not for your home DIY'er then!

[Neil Davidson]

Originally Posted by Malice

The SoundPro Audio Analyzer weighs in at about $2,000.
Not for your home DIY'er then!

Malice, you forgot the DAG 5161 digital audio generator which is the other half of the system. It also lists at $2000 .

LOL - that is why I do it for a living, not just for fun!

Neil

[Neil Davidson]

Russell,

For me the Audessy system has a few advantages.

1. Supports multiple microphone positions for calculated spatial average.
2. They have gone out of their way to explain how their system works.
3. I believe some models allow manual edit of the EQ settings via PC.
4. The "big daddy" separate Audessy EQ unit is awesome

Note above that I have not made any claims that the system is more or less accurate than any of the others I have tried, just that I like it more.

As to your problem, I don't think that Auto EQ is the answer. To get the phase set correctly on the sub you need to have the mains set with their final settings if possible. Then it is a process of integrating the sub to the system rather than the system to the Sub which it seems to me would be the result of your approach.

My method is to position all speakers where I want them then use the SoundPro or DAG to apply an impulse signal which starts a timer which stops when the impulse is recorded by the microphone. This of course then takes the full chain in to account allowing delays correct to 1ms to be acheived at the listening position. With this correct you can then set the sub phase correctly (as the final part of the sub setup) for smooth transition at the cross over point.

Without the closed loop measuring aspect I am unsure of how you could remove the reliance on Auto EQ to add the correct system delays as well as speaker distance delay.

Neil