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Centred mono signal appears to the left

Postby jellyjim » Thu Jan 14, 2021 6:56 pm

Evening

If I have a mono signal at pan 0 and it sounds dead center on headphones but towards the left on my monitors (I've just had to move studio rooms) then could the cause be that there's more space behind my left monitor (it's about three foot from an alcove to it's left) and less space behind my right monitor (it's effectively cornered by a wall and a tall shelving unit to its right) and might this effect be more noticeable on some frequency ranges than others; I'm looking at you, Mr Low End!

Thanks
Jim
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Re: Centred mono signal appears to the left

Postby MOF » Thu Jan 14, 2021 7:28 pm

Low frequencies are harder to locate so it’s unlikely to be that.
Swap the speaker feeds to see if the apparent pan position changes. I think it’s most likely a level difference on the speakers.
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Re: Centred mono signal appears to the left

Postby blinddrew » Thu Jan 14, 2021 7:28 pm

Certainly could be that. Swap speakers and cables over just to check that there's nowt wrong there but most likely it's the room.

EDIT - dispute between me and MOF! :D
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Re: Centred mono signal appears to the left

Postby awjoe » Thu Jan 14, 2021 8:00 pm

If you've got spare absorbers, maybe from another part of the room, stack them in front of the alcove and see what happens. If it removes the difference, it's not just a diagnostic, it's a fix.
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Re: Centred mono signal appears to the left

Postby Hugh Robjohns » Thu Jan 14, 2021 8:20 pm

From your thread title I was going to suggest you had a Mid-Side decoder in the signal path.... But it would seem the problem is more likely to be down to room acoustics.

Asymmetry, corners and open spaces can all seriously degrade and confuse stereo imaging through additional or absent reflections and boundary effects. And the apparent image offset will vary with frequency.

But if you've just moved rooms there's also the chance of cables being damaged, connections being tarnished, or control settings being disturbed.

So step one is to check the speaker sensitivity controls and cables, and swapping the speakers over is a handy quick way of seeing whether the problem is related to the room or the gear.

If the problem persists, then trying to improve the room symmetry and match the boundary conditions around the speakers would be a good idea.
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Re: Centred mono signal appears to the left

Postby jellyjim » Thu Jan 14, 2021 8:35 pm

Thanks all and thanks Hugh

Initial examination of cables/settings look ok but I will be thorough.

Room treatment is at colleagues studio space temporarily. Groan.

Hugh Robjohns wrote:If the problem persists, then trying to improve the room symmetry and match the boundary conditions around the speakers would be a good idea.

Is there any way of 'faking' this just to check? Like cutting a cardboard box diagonally, like a hood, and hanging it over each monitor? Or blankets? Just some way of quickly creating identical boundary conditions without hoofing everything around again!

Might be worth comparing volume levels too. Lower levels, fewer reflections?
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Re: Centred mono signal appears to the left

Postby Hugh Robjohns » Thu Jan 14, 2021 8:40 pm

Hang duvets around the sides and rear?
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Re: Centred mono signal appears to the left

Postby jellyjim » Thu Jan 14, 2021 8:41 pm

Hugh Robjohns wrote:Hang duvets around the sides and rear?

Ok cool, if you think that's sufficient. Wasn't entirely sure if I had my science right. I'll give it a go!
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Re: Centred mono signal appears to the left

Postby MOF » Thu Jan 14, 2021 9:40 pm

Is there any way of 'faking' this just to check?
Play a loop of some music at a sensible level and put your ear up close to each speaker in turn, if they sound the same then that's a quick way of excluding the acoustics.
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Re: Centred mono signal appears to the left

Postby MOF » Thu Jan 14, 2021 9:41 pm

EDIT - dispute between me and MOF! :D
Pistols at dawn. :lol:
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Re: Centred mono signal appears to the left

Postby jellyjim » Thu Jan 14, 2021 9:42 pm

MOF wrote:
Is there any way of 'faking' this just to check?
Play a loop of some music at a sensible level and put your ear up close to each speaker in turn, if they sound the same then that's a quick way of excluding the acoustics.

D'oh! That's a very good point :) I'll put the scissors and cardboard boxes away.
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Re: Centred mono signal appears to the left

Postby jellyjim » Thu Jan 14, 2021 9:43 pm

MOF wrote:
EDIT - dispute between me and MOF! :D
Pistols at dawn. :lol:

Don't start early on my behalf. That's have elevenses first.
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Re: Centred mono signal appears to the left

Postby CS70 » Thu Jan 14, 2021 9:54 pm

Stereo image messed up by reflections, different equalization/level on the speakers, bad cables, monitor controller settings... Could also be one of the monitors getting dodgy - it happens sometimes when you move electromechanical stuff. Check that the XLRs are well locked in, you never know.

You don't say what mono signal but the fact that it's so noticeable suggests a that the shift is on a quite large frequency band - so I wouldn't think of reflections and resonances are likely to be the most probable cause, but rather any of the rest. My own monitors at home (KH120, so ports in the front) have extremely asymmetrical space on the sides like yours, with one being very near the side wall, but apart level and a little equalization the stereo image is pretty alright.

Duvets or other makeshift absorbers can come handy to test, as the others said.
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Re: Centred mono signal appears to the left

Postby MOF » Thu Jan 14, 2021 10:07 pm

EDIT - dispute between me and MOF! :D
Pistols at dawn. :lol:

Don't start early on my behalf. That's have elevenses first.

It just sounded more dramatic, in truth I'm not an early bird, so mid afternoon would be better. ;)
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Re: Centred mono signal appears to the left

Postby jellyjim » Thu Jan 14, 2021 10:11 pm

I downloaded a sound level meter app for my iPhone and created a 440hz sine wave test tone in Audacity and measured same distance from each monitor (about 10cm) and got 74.9 vs 76.2 Instantaneous level dB(A).

A significant difference or negligible? They certainly sound the same up close and if I sit back in my normal monitoring position I get the same left bias as the bass lick in the song I was working on.

I did make a video with my iPhone to try and illustrate the sound in my room and weirdly the bias wasn't evident so I exported the audio from the clip to look at the waveforms ... and realised the iPhone records in mono! :headbang:
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