MultEQ managed overlap to treat SBIR

It has been suggested[1] that just as more subwoofers can be used to compensate for SBIR it could beneficial to have the sub and the main speakers overlap for the same reason.

Audyssey seem to have firm belief in this not being the case and that a clear cross over with no overlap is desired in all cases. (I'm basing this on the two statements that speakers should always be set to "small", and that "double bass" will create "muddy" bass)

I'm curious, is this disagreement based on pure theory only or is there a dimension of technology failure involved? Could Audyssey, in theory, make MultiEQ manage the overlap in a non-muddy way?

In my case I have an Onkyo TX-NR3008. If I would set the speakers too "Full Range" and enable "Double Bass" I would effectively disable both low and high pass filters, while sending all signals to the sub (true?). So with this setup, MultiEQ would be in full control of setting low and high pass filters (true?). Thus the only thing needed to properly treat some unfortunate SBIR dips I have in the 50-120Hz range would be for MultiEQ to calculate the proper filters, a simple matter of a firmware update to enable (true?)

Given that my assumptions above are correct. Is this something you would consider developing for a future upgrade?

[1] http://www.hifizine.com/issues/bass-integration-guide/

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7 Comments

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    Chris Kyriakakis

    Yes, I completely agree that the crossover should be done in MultEQ.  We have actually developed and showed this, but they have not agreed to put it in yet.  It's the right way to go.

    The reason to look at the blend is that the decision of crossover should really be based on a multiposition measurement across the listening area.  That involves some weighting of the responses.  

  • 0
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    Chris Kyriakakis

    Hi John,

    The DSP chip in the AVR has many functions to perform.  Only a few are related to Audyssey.  The Double Bass feature sums the bass from all channels and basically y-cords it internally to the subwoofer channel and back to the Full Range speakers.

    MultEQ can see the subwoofer just fine.  It can also see every other speaker individually.  What it can't see is the blend of a speaker and sub.  To do that it would have to ping the speaker and sub together through the crossover filter in the AVR.  That has not yet been possible from the AVR makers.

    MultEQ processes the signals sent to the speakers.  It doesn't care what the source is.  If there is signal sent to a speaker (directly or via upmixing) it will be processed by MultEQ.

    Regarding your lat question: that's our CES announcement next week!

  • 0
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    John Nilsson

    That CES announcement sounds exciting looking forward to it :)

    Thank your for patiently answering my questions by the way, I's sorry if I seem a bit dense, just really curious by nature ;)

    I'm still a little bit confused though. In my original suggestion there would be no AVR provided crossover. The entire idea was for MultiEQ to implement that. In my mind the MultiEQ algorithm works with a virtual model of how things should sound when mixed. The measurements at setup time is done for each speaker individually no? Even when two subs are involved I assume there is no empirical trial and error performed on how those blend. So I don't really understand why you say it needs to look at the blend?

    It knows the upper limits of the sub and the lower limits of the other speakers. Would not a simple sum of the measurement results suffice to create model of how things overlap? Is this not already done when the system has two subwoofers?

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    Chris Kyriakakis

    Hi John,

    The crossover filters are now a standard used in every AVR.  They are what's called Linkwitz-Riley filters and involve a 2nd order highghpass and a 4th order lowpass.  This has been shown to preserve the phase and produce a perfect blend.

    Bass management = distributing the bass to the satellites and subs.  Audyssey has no role in that.  Sadly, it comes after MultEQ in the audio path and so Audyssey can't do anything more advanced in the overlap region.  Perhaps in future AVRs this would change and then there are a number of other things we could to produce an even better blend.

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    John Nilsson

    If understand this correct a Linkwitz-Riley filter is a mathematical model, and as such can be implemented either through analog hardware or by DSP. Such a DSP could, for example, apply a low pass butterworth filter to the subwoofer channel, and matching high pass filters to the other channels.

    This depends on two things though: 1. The DSP is in control of all channels, and 2. The subwoofer channel contains a full range mono mix to filter in the first place.

    The full range mono mix is "enabled" by the "double bass" feature but unfortunately, if I understand you correct, the DSP is not in control of that channel. As far as the DSP is concerned there is no subwoofer channel as it hasn't been created yet.

    Correct so far?

    If MultiEQ can't see the subwoofer, how can it provide room correction for the separate subwoofers and speakers in the system? Is it simply assuming that any signal below the configured crossover will be sent to the subwoofers and then applies the same filter to all channels? How can it then provide different corrections for two different subs in the same system?

    Exactly what channels do MultiEQ control? The original source channels? So for a 2.0 it has to assume front speaker output with the potential subwoofer if a crossover has been configured? What if I have some up-mixing DSP mode enabled?

    Speaking of up-mixing DSP modes, if other DSP applications in the AVR can up-mix a signal to other channels, what stops audyssey from doing the same? Would it not be possible to provide an Audyssey Stereo mode that converts 2.0 content to 9.2 to provide the optimum bass managment? (11 "subwoofers"!!!)

  • 0
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    Chris Kyriakakis

    The muddy bass from a bad overlap has nothing to do with Audyssey.  It's well established in the peer-reviewed research literature that bass management provides the proper blend.  In fact, very specific highpass and lowpass filter types have been shown to be the optimal filters to preserve magnitude and phase smoothness through the overlap.

    MultEQ has absolutely nothing to do with bass management or setting highpass and lowpass filters.  That is done by the AVR.

    Double Bass is a pure marketing idea that caters to people who feel "insulted" when their speakers are not set to Large (Full Range).  This has been told to us numerous times by the AVR makers.  It's only there to please these customers, but has no basis on science.  

  • 0
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    John Nilsson

    It was not my intention to imply that Audyssey creates a muddy overlap. I'm assuming that muddyness is simply the result of blending signals with different characteristics and alignments.

    When you say that "very specific" filters are needed, do you then mean that specific hardware controlled by the AVR is required, and that this is not available for the audyssey filters?

    When you say MultiEQ has nothing to do with bass management, could you please elaborate. I think I've misunderstood some definition of terms here. With bass management I was thinking of mode and SBIR compensation in the bass through DSP. Did you simply mean bass management to equal setting a crossover filter?

    I understand that "Double Bass" is a marketing thing. I also understand that with no further modifications of the result is simply an unmanaged blend of signals, with resulting muddyness.

    My thinking was that if you have two subwoofers, multieq ensures that they blend in a proper way given their positions and the room characteristics.

    Why then could not multieq do the same if it could use the overlap from other speakers just as if it was another subwoofer?

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