... does it have a problem?

We've been using a Yamaha MG32/14FX for our church sound for a while now, and today I was doing some general tidying up after a week of local schools using the church for their Christmas events.

Can someone confirm I am right in the above assumption and not going mad:

If I plug in a source on an input (in this case the CD player) and turn up the input gain so it is just peaking and then back it off a tad, and then check that channel with the PFL switch, the PFL meters do show that input peaking at 0dB. OK. Switch out PFL and raise the channel fader to 0dB and the master stereo fader to 0dB. Shouldn't I have the meter showing the signal peaking at 0dB? - As far as I can see, I have unity gain through the signal route... Yes?

So why am I only getting -8dB or something?

Should I be getting the desk serviced?

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New album 'Fantasy Bridge' available now!
Making of Fantasy Bridge Diary

Quote MarkOne:

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If I plug in a source on an input (in this case the CD player) and turn up the input gain so it is just peaking and then back it off a tad, and then check that channel with the PFL switch, the PFL meters do show that input peaking at 0dB.

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Personally, I'd have pfl'd the channel in the first place and then adjusted the gain to provide a sensible level on the meter... but yes, you've set the input gain to establish a sensible headroom.

Quote:

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Switch out PFL and raise the channel fader to 0dB and the master stereo fader to 0dB. Shouldn't I have the meter showing the signal peaking at 0dB?

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Not necesarily. It depends on several things.

1. The EQ can affect the overall signal level dramatically if the controls are set to anything other than unity gain.

2. Anything plugged in to the insert point could affect the gain.

...although either of these should be observable on the PFL meter, of course.

3. If you're using a mono channel, the pan pot will affect the channel level.

4. Whether mono or stereo channels in use, the routing will affect the levels -- specifically, if you are routing via a group rather than (or as well as) straight to the main stereo output.
the routing.

5. If you are going via the group then the group fader and pan will have an effect, as will anything inserted into the group insert point.

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Should I be getting the desk serviced?

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It's not very likely that a fault would produce a clean 8dB loss of level. It's more likely that a fault would sound nasty or not sound at all.

I suspect either finger trouble with group routing or pan pots. The handbook for the mixer includes a signal path level diagram that might help in understanding where the signal is getting lost.

Hugh

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Technical Editor, Sound On Sound

thanks for the reply Hugh.

So, there is nothing on that channel insert, and the EQ is set flat, and as you say, anything affecting the gain there would show up on the PFL meter.

It's a stereo channel, Pan is set to 0, and it is routed straight to (and only to) the master stereo output and all the aux sends are turned down.

This is weird!

I will as you say dig out the manual and look again at the routing diagram..

... er... has anyone seen some missing dB lying around?

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New album 'Fantasy Bridge' available now!
Making of Fantasy Bridge Diary

Sounds like you need to get a test tone source out and follow the levels through the signal path. There are plenty of test CD's around with suitable reference tones, or you can use a synth patched with a nice sine wave.

It would be helpful if you have a second device handy with a good audio meter. Plug the source into that device and adjust the output level of the source to get something sensible, like +4dBu (0VU)

Next, plug it into the mixer and set a level on the input using the PFL to get a steady +4dBu (0VU) as well.

Now make sure the balance control is in the centre, EQ is byspassed or zero'd, stereo fader is at unity, route to the stereo output and PFL the output (if you can). Failing that, set the output fader to unity and check the output meters and the output AFL. Note the meter readings.

Now connect your earlier meter device to the mixer output and see how they compare. Ideally, the reading at the mixer out should be the same as the original input becasue everything is set to unity.

If it's not, adjust the channel fader to bring the desk output meter to +4dBu (0VU) and see what the reading is on the connected meter device.

That was, you can check where the signal loss is occuring, or whether it is a desk output meter alignment issue.

Hugh

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Technical Editor, Sound On Sound

Hi, does the desk have headphone monitoring for channels and output? If you can compare the signal over cans from the channel to the master output and the output is much noisier then maybe(and only maybe) do you have a problem.If the sound quality remains consistent then somewhere summat is up but it doesnt sound like a fault.Dave

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My head hurts!

6dB pan law and 2dB master buss attenuation?

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planet nine
lincoln, uk.

Numpty question : Could Yamaha have deliberately set this up so that the desk's stereo bus effectively has 8db of headroom? More along the lines of a safety buffer.

Or is that just plain silly ..?

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Veni, Vidi, Aesculi
(I came, I saw, I conkered)

Quote Dave B:

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Numpty question : Could Yamaha have deliberately set this up so that the desk's stereo bus effectively has 8db of headroom? More along the lines of a safety buffer.

Or is that just plain silly ..?

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It isn't silly.

I am actually leaning towards Nathan being close if not completely correct. It is not uncommon for summing points to be designed like this as otherwise for each full signal you send into it you wil be adding 3dB to the summed signal, and it won't take much to overload a bus.

I have one of these boards in my third space, Ill take a look at it when I get a moment, but I am so busy right now I don't know how long it will be. I do believe the behavior noticed by the OP is intentional by Yamaha though.

Seablade

Seablade and Nathan are almost certainly right. My Yamaha MG-206C does exactly the same.

Thanks guys, at least it just looks like that's the way it should be.

I'm guessing that a mix bus with loads of headroom is one of the things that marks out the higher end kit from the mid level stuff like ours.

At least I'm not going mad (well no more that usual )

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New album 'Fantasy Bridge' available now!
Making of Fantasy Bridge Diary