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Mic / SB Matrix Time/Phase Shift

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d5:
Apologies if this has been covered before, but I did a search and while it's certainly mentioned in passing, I didn't see a thread directly addressing this.

I've recently started running 4 tracks; stereo audience microphone and stereo SB and I've spent some time calculating what I predicted the time shift would be and then actually making adjustments and it comes fairly close.

On one particular recording, the mic's were set about 2 meters from the stage and approximately 4 meters from the mains. On paper this seems to be about a 11ms shift (11ms = 12/343) to earlier for the aud/mic's. When I make the adjustment by visually comparing the tracks, I come up with about 9ms.

I suppose there are all sorts of phase problems with doing a matrix and this only compensates certain aspects, but was hoping to get other opinions on approaches. Also, i'm using Audacity to make the adjustment. Also, visually comparing tracks is not exactly a science, wondering what others do here.

Thanks,
John

LoveBuzz81:
Time = Distance/Speed of sound (1,126 ft/s)


sample:

4 ch matrix mix: stereo pair is located 30 ft. f/ the PA and SBD mix.

30 (distance)/1126 (speed of sound) = 26 ms (time)

add 26 ms sample delay to the sbd mix.

ScoobieKW:

--- Quote from: LoveBuzz81 on March 26, 2017, 06:35:19 PM ---Time = Distance/Speed of sound (1,126 ft/s)

--- End quote ---

At sea level, with a certain barometric pressure. Due to these variables, a millisecond per foot works to get you close, then lining up by eye is helpful.

if your mics are onstage or close, often a phase flip of the board channels will be enough, take a listen and judge for yourself.

Gutbucket:
In addition to air-travel time/distance, digital processing and recording will cause some small but significant delay of signal.  That can potentially affect things on both sides of the equation  - on your side for the recorders, which is probably only significant if you are using different recorders for AUD and SBD, and on the SBD side due to a digital board or FOH processing which is probably more common.  It won't be much but it can be several milliseconds.

Calcs help get close, visual alignment helps get close.. yet the best way I know is to get close via those methods then make a final alignment decision by ear while nudging things back and forth a bit listening for what works best.  For me stage banter is the most optimal material to use for detecting alignment issues by ear, we are super attuned to hearing detail and echo on human voice so as to be able to extract speech content, and there generally is no other conflicting content while the band members are talking to the audience so any misalignment becomes easier to hear.

goodcooker:

I follow the "roughly 1 ms per foot or less" rule then line up by ear. You can hear comb filtering in the bass frequencies when you are off. When the snare  drum sounds tight and the kick drum and bass guitar have good presence with no smear I call it good. I also utilize the wave scope in Wavelab. There may be a plug in for Audacity.

If you are using a coincident stereo mic and the SBD is run in mono you can line them up just by looking at the scope which will show a straight up and down line indicating mono compatibility.

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