How does MultEQ apply room correction?

The technology is a result of a multi-year university research effort to understand the key factors that influence sound reproduction.  From this research came two key findings:

1. Acoustical problems in the room are more accurately measured in the time domain.  This type of analysis provides information about the direct sound and the effects of reflections from room surfaces.  This was a departure from traditional EQ methods that only looked at data in the frequency domain.
2. Measuring in a single location does not capture sufficient information and often results in equalization artifacts.  Multiple measurements are required to capture the spatial distribution of acoustical problems, particularly in the low frequencies where the problems are more serious.

MultEQ captures multiple measurements in the time domain and then groups them in clusters based on similarities in the data.  Using Fuzzy Logic mathematics, the clusters are allowed to overlap so that each measured response belongs to each cluster with a certain probability.  In each cluster a representative response is then created that is weighted by the acoustical problems in that cluster, but also by those in the other clusters.  MultEQ then re-combines these representative responses to create a final room representation and then inverts that to create the correction filter for each loudspeaker.  The type of filter used by MultEQ simultaneously corrects the time and frequency domain problems to produce a smooth response.

MultEQ also measures the time it takes for the signal to arrive from each speaker to the first microphone position.  Delays are then applied to the speakers that are closer to match the timing of the signals coming from the speakers that are farther away.  Finally, the sound pressure level produced by each speaker is adjusted with the trim controls so that they match each other.

Hi Chris,

I was wondering what happens to Audyssey when I throw an SACD in my player. I don't see the "Audyssey" logo appear on my A/V rec...just the "DSD"...would I need to go back and manually configure a sub?

Thanks

Audyssey is applied to any input that the manufacturer allows.  If the connection is digital and not through the analog multichannel input to the AVR then it should be on.  Most AVR models don't have A/D converteres on the multichannel inputs and so no processing is applied to those.  But, it sounds like you are using a digital connection.  It's best to check with the manual of your product to see if they have any restrictions on processing for certain types of sampling rates.

Hi. Following up on the question above, I have read that for DSD sources (i.e., if SACD is passed over HDMI in DSD format), that a processor or receiver with Audyssey will first convert the DSD to lower resolution PCM in order to apply the Audyssey correction?  Is this correct?  If it matters, I have a Marantz AV8003 processor.

Thanks.

Hi Kevin, this is out of Audyssey's control. Every AV maker decides what to do with SACD signals before sending them to any internal digital process including Audyssey. As you know DSD can not be processed in any way as is.

My head is reeling from reading your first paragraph! Nice try, but can you have another go with a flow chart and/or pictures of waveforms, data,. Eg what is measured? (amplitude?), And Groups what into Clusters? A picture paints a thousand words....

Hi Wayne,

Are you sure the head spinning is not an after effect of New Year's libations?  :-)

More pictures here:

http://www.audyssey.com/audio-technology/multeq/tour

You may have a point, thanks for quick feedback. I have reviewed the Tour, much appreciated. I have been doing back ground reading, I am very impressed with my AVR for movies, but struggling to achieve the same for music. I will read more FAQ, and see where that gets me. Cheers ;-)

Hi Chris, I just have one quick question. Well at least the question is quick the answer may not be. In my reading and discussions on various forums etc. Some people often state that trying to correct the high frequencies is a waste and more often than not is detrimental to the sound. They often site Floyd Toole as their source. My understanding is that is correct when talking about traditional methods such as graphic and parametric EQ solutions but does not apply to how Audyssey, Trinov, ARC, etc. apply correction. How do you respond to that when asked?

Hi Jeff,

The answer you allude to is part of the reason. Traditional EQ methods with parametric or graphic EQ are based on filter bands that have increased phase anomalies as they get narrower.  I can't speak for Trinnov and ARC because I don't know the type of filters they use. But, Audyssey uses time domain measurement and correction and the resulting filters are not based on bands.  Instead they operate on the amplitude and phase of the signal simultaneously to avoid any such anomalies.

There is other research (in addition to our own) from the BBC that shows the importance of equalizing speakers all the way up to beyond 10 kHz.  In fact, the BBC work showed that a ±1 dB match is required between speakers otherwise stereo imaging suffers.  Even the best speakers have difficulty matching each other to within such tight requirements when placed in different locations in the room.  Correction all the way up to the highest frequency range can fix that if properly applied.

Thanks Chris. 

Hello Chris,

I have noticed that audyssey at least for me adds some bass or deeper frequency to voices making them sound a bit boomey. I guess it’s the whole sound image that is affected but I can hear it especially with voices. When I switch audyssey on and off I can hear quite a big difference in the bassyness or deepness of voices. The increased bass comes from my center speaker and not subwoofer or anything like that.

Is this maybe a normal loudness function of audyssy to boost the lower frequencies? Is there anything I could have been doing wrong during setup that could cause audyssey to overcompensate in this regard?

Hi Jens,

Audyssey MultEQ is purely for acoustical correction.  It tries to reproduce a flat frequency response with no low frequency boost and a slightly rolled off high frequency response to match the studio listening conditions.

Audyssey Dynamic EQ is a human loudness compensation technology.  It will boost the bass gradually as you turn the volume control down from 0 dB reference.  It uses film standards as its reference.  However, music content is not mixed to the same standards and so it may need a reference level offset.  This is explained here.

Hello Chris,

One of my friends asked me if Audyssey MultEQ XT32 tries to control resonance? Due to I am not so advanced in audio, I decided to ask you.

Also, if I connect power amplifier, will Audyssey make some other corrections other then gain adjustment during recalibration of a system?

I am not really sure what they mean by "resonance".  Audyssey measures and corrects the frequency response of the system and the time domain problems due to unwanted reflections in the room.  The gain adjustment is a small and almost insignificant part of the correction.  It's the room correction filters that are the most important.

Hi Chris,

Currently using 7.1 (and DSX) w/ videos.  However, I might have to temporarily move down my 2 front-wide speakers for audio use in the living room.  That would mean I'd be back to 5.1 setup (but no movement of the remaining 5.1 speakers).  Does this require me to run Audyssey calibration again, or can I just remove the 2 front-wide speakers w/o affecting the current calibration?  Thanks again.

Hi Joel,

If you simply turn off DSX and remove the Wides there is no need to run the calibration again.

Multi EQ and Custom EQ:

If I edit and create my own EQ and set Audyssey to "Manual", I notice Dynamic EQ gets set to OFF.  What other Audyssey features are still active?  Is the crossover still Audyssey or is it the Marantz (in my case) crossover?

Is there a way to set a custom/manual EQ and still have Dynamic EQ?

Thanks.

There is no Manual setting for Audyssey MultEQ.  Once you select Manual you switch to simplistic parametric/graphic EQ filters and the Audyssey MultEQ filters are turned off.  All other Audyssey technologies are turned off as well.  The levels, distances and crossovers still remain.