Level-Matching Pre-Dirac, AGC, and Line-of-Sight

[barrak]

Many users have reported one or more of the following symptops, which I believe are related to the same issue:
a) Lower volume level post-Dirac filters.
b) Inferior results when AGC is On.
c) Inferior results when obstacles block speaker/mic line of site. For example, seat back blocking a surround/rear speaker.

In an ideal situation, you will have a trifle or none of these issues if the output volume calibrations for all speakers (and sub) result in the exact reference level. Most of us have independent level controls only on the sub, and some don't even have that. The lucky ones would have a way to control the level of each speaker as well (at the amp or an active speaker, not from within the XMC-1).

Years ago, Tact users struggled with this issue and suffered mainly from (a) above. In Tact setup, the mic is connected to the processor direct, so AGC was not an issue. Further, procedure required measurements at ear level alone so (c) was not an issue either, for most.

The issue in (a) above caused another problem that I haven't seen mentioned in this forum yet. When Dirac processing is forced to reduce overall volume due to measurement level imbalances, it does so in the digital domain. As far as I know, this means loss of overall dynamic range (or lost bits) and coarser articulation of audio nuances.

What I would suggest is the following:
1. Do your best to level match your speakers/sub during the calibration process using whatever post XMC-1 means available to you; amp controls, LCR toe-ins/tilts, surrounds/rears relocation/in-line attenuators, ...etc.
2. At least the primary spot and elevated mic positions should not be obstructed from any speaker (sub is OK). I would venture to guess that Dirac expects the mic to be blocked from surrounds/rears in the lower mic positions and would adjust processing accordingly.
3. If you have multiple subs (and unless you know exactly what you're doing and have the means to balance their phases, latencies and room interactions), stack them vertically at a location that would give you the least null-to-peak swings.


Would love to hear your feedback.

[tunatamer]

For me, raising my measurement positions as per LSC's recommendation solved A and C.

[rswood]

Jan 24, 2015 11:26:14 GMT -5 barrak said:

Many users have reported one or more of the following symptops, which I believe are related to the same issue:
a) Lower volume level post-Dirac filters.
b) Inferior results when AGC is On.
c) Inferior results when obstacles block speaker/mic line of site. For example, seat back blocking a surround/rear speaker.

In an ideal situation, you will have a trifle or none of these issues if the output volume calibrations for all speakers (and sub) result in the exact reference level. Most of us have independent level controls only on the sub, and some don't even have that. The lucky ones would have a way to control the level of each speaker as well (at the amp or an active speaker, not from within the XMC-1).

Years ago, Tact users struggled with this issue and suffered mainly from (a) above. In Tact setup, the mic is connected to the processor direct, so AGC was not an issue. Further, procedure required measurements at ear level alone so (c) was not an issue either, for most.

The issue in (a) above caused another problem that I haven't seen mentioned in this forum yet. When Dirac processing is forced to reduce overall volume due to measurement level imbalances, it does so in the digital domain. As far as I know, this means loss of overall dynamic range (or lost bits) and coarser articulation of audio nuances.

What I would suggest is the following:
1. Do your best to level match your speakers/sub during the calibration process using whatever post XMC-1 means available to you; amp controls, LCR toe-ins/tilts, surrounds/rears relocation/in-line attenuators, ...etc.
2. At least the primary spot and elevated mic positions should not be obstructed from any speaker (sub is OK). I would venture to guess that Dirac expects the mic to be blocked from surrounds/rears in the lower mic positions and would adjust processing accordingly.
3. If you have multiple subs (and unless you know exactly what you're doing and have the means to balance their phases, latencies and room interactions), stack them vertically at a location that would give you the least null-to-peak swings.


Would love to hear your feedback.

I would be very interested to know if your number two was correct that dirac compensates for lower placement with rear speakers.

if it does compensate would it then be incorrect for rear speakers that have a clear line of sight?

[rogersch]

Turned AGC off. Raised level off measurement (now line of sight and not too close to the sofa). Audio level of DIRAC nearly identical to non DIRAC.
A happy user.

[aud]

Jan 24, 2015 11:26:14 GMT -5 barrak said:

Many users have reported one or more of the following symptops, which I believe are related to the same issue:
a) Lower volume level post-Dirac filters.
b) Inferior results when AGC is On.
c) Inferior results when obstacles block speaker/mic line of site. For example, seat back blocking a surround/rear speaker.

In an ideal situation, you will have a trifle or none of these issues if the output volume calibrations for all speakers (and sub) result in the exact reference level. Most of us have independent level controls only on the sub, and some don't even have that. The lucky ones would have a way to control the level of each speaker as well (at the amp or an active speaker, not from within the XMC-1).

Years ago, Tact users struggled with this issue and suffered mainly from (a) above. In Tact setup, the mic is connected to the processor direct, so AGC was not an issue. Further, procedure required measurements at ear level alone so (c) was not an issue either, for most.

The issue in (a) above caused another problem that I haven't seen mentioned in this forum yet. When Dirac processing is forced to reduce overall volume due to measurement level imbalances, it does so in the digital domain. As far as I know, this means loss of overall dynamic range (or lost bits) and coarser articulation of audio nuances.

What I would suggest is the following:
1. Do your best to level match your speakers/sub during the calibration process using whatever post XMC-1 means available to you; amp controls, LCR toe-ins/tilts, surrounds/rears relocation/in-line attenuators, ...etc.
2. At least the primary spot and elevated mic positions should not be obstructed from any speaker (sub is OK). I would venture to guess that Dirac expects the mic to be blocked from surrounds/rears in the lower mic positions and would adjust processing accordingly.
3. If you have multiple subs (and unless you know exactly what you're doing and have the means to balance their phases, latencies and room interactions), stack them vertically at a location that would give you the least null-to-peak swings.


Would love to hear your feedback.

"3. If you have multiple subs (and unless you know exactly what you're doing and have the means to balance their phases, latencies and room interactions), stack them vertically at a location that would give you the least null-to-peak swings."


After you run your DIRAC measurements you will have to keep the two subs, that are vertically stacked, in place. If you move one of the subs back to its original position you will have to run DIRAC again. Because of this I would not recommend it. Unless, barrack is saying to leave them stacked after the measurements.