DIY Phase Meter?

[shrike]

[quote author="shrike"]I'm still a little unsure as to the difference between how MCI/Sony implement their PCMs and how Neve/SSL do. . . Could you explain it again for the dense I've read your first reply about 50 times and still can't figure out where you're talking about MCI/Sony and when you're talking about Neve/SSL. . .[/quote]

I should have previewed. What crap grammer/punctuation! I can rite gud, eye swer!

Take Two: I'm still a little unsure of the differences between how MCI/Sony implement their PCMs and how Neve/SSL do. Could you explain it again for the dense? I read your first reply about 50 times and still can't figure out when you're talking about MCI/Sony and when you're talking about Neve/SSL. . .

 

[SSLtech]

Oh, I never really got into the details of how they do it... Scenaria came inand distracted me... I told him I was in the middle of something, but you know how he is!!! :wink: ) Neve and SSL do it slightly differently, but they noth work well. At silence the Neve reads 100% in-phase (silence doesnt disagree with itself, so it muse be in-phase!) Nothing wrong with that. SSL at silence sits in the middle. Neither in nor out of phase... nothing wrong with that either. Same signal fed to both they both usually read the same and agree.

From memory, Neve generate a full-right diflection voltage and "subtract from it" the amount of disagreement between the two channels, in CMOS from what I remember, very likely using a similar method to the ons used in Frank's pdf. SSL did it differently, (and rather more expensively from memory, though the less expensive Neve version works exactly as wel) I'm trying to dig up a schematic if I can.

My DK has switchable response (fast/slow) and that's the only difference between it and the others in the single correlation value display. (not hte scope waveform part)

MCI/Sony, -I never looked at their schematic, because it behaved so badly that I never wanted to copy any part of it!!! However on our 3036, if you take a 1kHz signal panned center, it reads fully to the right -Hoorah! -If you start to pan it left or right, it starts to lean to the center a bit. -Now Fully right is +180° (which is in my book the same as -180°, which would be all thge way to the left, but even overlooking that marking error, the same 1kHz at differing amplitudes in two channels should still be just as completely in-phase as if hte amplitudes were equal. -I suspect that they made the same sort of erroneous assumption somewhere in the design that others have suggested in this thread... Just a guess though.

Keith

 

[Guest]

[quote author="PRR"]> I'd like to build.. a Phase Correlation Meter
What you want is a 2-D display. A CRT, not a meter.
Feed one channel to the X (normal) input, the other channel to the Y (horizontal) inputs. Trim to about equal gain. Feed the same signal to both inputs, you get a straight line slanted 45 degrees.
[/quote]
Thats good idea, it was really used in great analogue consoles from
1970-ies. It is nice to see picture of soprano solo miked by some distant mic (AB) pair
And I have seen digital (distribution) console (it is used in distribution room where modulation is distributed to th transmitters), and there
was big plasma display with that corellogram. Very nice It was Studer,
if I remember correctly.

But simple corelometer is generally four - quadrant multiplier with R and L inputs followed by integrator and deprez meter with zero in the middle.
in better equipments there is also two quadrators for R*R and L*L
followed by integrator and going to divisor - then you have +1 0 - 1 scale
independent to signal amplitude.
It can be done as a linear bargraph. It is useful at FM transmitter
to check, if you have R/L phase O.K.

xvlk

 

[SSLtech]

Well, Hope I don't get killed for this, but here's the rether more complicated SSL way of doing things. Presented here so that people can appreciate another approach. For DIY-ing, I recommend the much simpler approach taken in Frank's pdf

Keith

 

[bcarso]

[quote author="SSLtech"]Well, Hope I don't get killed for this, but here's the rether more complicated SSL way of doing things. Presented here so that people can appreciate another approach. For DIY-ing, I recommend the much simpler approach taken in Frank's pdf

Keith[/quote]

Where?

 

[SSLtech]

Oh... um.... isn;t it obvious?

...

...well, if I have to spell it out for you... :wink:

RIght click, save-as... won;t be there forever and all that stuff... :wink:

-(sorry I forgot the link! )

Keith

 

[Guest]

[quote author="SSLtech"]

[/quote]
Maybe this something do, but it looks like
phasemeter, not corellometer ????
May be approximative???
Or am I so stupid ?

xvlk

 

[SSLtech]

I don't understand the distinction, -is it a language difficulty perhaps?

This is a center-zero mechanical meter driver to display 100% phase correlation as full-right, and 0% correlation (100% decorrelated) as full left.

Keith

 

[Guest]

[quote author="SSLtech"]I don't understand the distinction, -is it a language difficulty perhaps?
[/quote]
Not language difficulty, system view dificulty.
It maybe works for sinus properly, but not for general signal.
Simply I can not imagine how to overcome multipliers and integrators with simple TTL stuff. Maybe it is because I am young and much DSP
directed. Honors to analogue circuit genius from the past!!!

xvlk

 

[shrike]

I think the problem is that when someone (like, say, ME) mentions a phase meter, people have different ideas of what that means.

I think I may have confused the issue by specifying a "Phase Correllation Meter", a term that I picked up while looking for schematics for the type of object Keith (and others) have been informing me on.

For example, http://www.mhlabs.com/products/sf_features.html describes a phase correllation meter as something that

. . . reduces the relative phase information between two channels to a number between -1 and 1.The centerline corresponds to a correlation of 0 while the top edge corresponds to +1 and the bottom to -1."

http://w3.studiotech.hu/studiotech/hu/audio/rtw/rtw140.htm describes it the same way.

I know that there are other Phase meters which use a CRT-type display, where perfectly in-phase signals show up as, say, a diagonal line (LL to UR). In my searching, those seem to be generally referred to as "Phase Scopes".

Of course, there's often a huge difference between the technical description of something and the lay or popular description of such. If I'm misusing a term, please forgive me. However, to the people who I haven't confused, thank you VERY much for your excellent input!

 

[SSLtech]

I think you're right on the money.

The DK audio stuff is a phase scope but it has a phase meter on the left side of the display...

Keith

 

[PRR]

> I should have previewed. What crap grammer/punctuation! I can rite gud, eye swer!

Reads "OK" to me. Better than some chatter on the board.

But if you must rite gud, and see you failed, and nobody has quoted your typos, hit the

button above your flawed post. You can edit any time, even years later, though editing to make subsequent posts from others look dumb is impolite, and editing after any reply will flag the edited-timestamp footnote.

 

[soundguy]

I dont mean to derail this and this is not a troll but an honest question-

with the exception of mixing for broadcast, what are the circumstances where a phase meter can help your mix?

Ive never used one before and outside of transmitter requirements Im having difficulty seeing how I would ever reference such a meter on my mix so Im curious.

thanks

dave

 

[chriss]

[quote author="SSLtech"][quote author="chriss"]

How about buying an old dual trace scope and hooking it up so that it Lissajous the left and right channels?

That could do fine but very many of these beasts do very unpleasing high-freq-noise, that would make mixing a no-fun job.[/quote]
... ... ...-really? -I very much doubt it.

Are you certain that you're not getting confused with regular, 'scanning' type CRT's? -I know that with a 'Television' type of CRT, the leakage from the scanning waveform sent to the deflection coils can cause what you're describing, but think about it, with X=L, Y=R (or vice-versa) the 'deflection' signal is the audio signal... there's no fixed HF scanning. Likewise for M/S displays.

Keith[/quote]

Ähh, no I'm not sure, maybe you're right. I was thinking of an osci in normal use with a ramp-generator.

Chris

 

[shrike]

PRR: D'oh! The message board I spend the most amount of time on has editing disabled, so it never occured to me!


[quote author="soundguy"]
with the exception of mixing for broadcast, what are the circumstances where a phase meter can help your mix?

Ive never used one before and outside of transmitter requirements Im having difficulty seeing how I would ever reference such a meter on my mix so Im curious.
[/quote]

Well, you know that when two signals are out of phase, you end up with certain freqencies getting attenuated; That's true regardless of whether or not you're mixing for a CD, in a club, or for broadcast audio. If (due to a delay effect, vagary of the recording, or something like that) your left and right signals (or front and back signals) start getting out of phase with each other, the result in the acoustic space is going to be less than optimal.

A phase meter used while mixing allows you to intercept problems like that and helps the engineer double-check against what they're hearing.

As to why to do that during mix? It's the antithesis of the "fix it on the recording"->"fix it in the mix"->"fix it in the mastering" mindset. If I'm paying attention to phase during mix, it means that I'm exerting more control OVER the mix, and leaving less for the mastering engineer to worry about. The less that needs to be done at mastering, the likelier that the end product will sound like I want it to.

Again, the meter is just a little aid to support the engineer's ears.

In some regards, my response to your question is "How can you NOT be concious of phase during mix? That's the most important time to be worrying about it!"

Does that help?

 

[SSLtech]

Working M/S or X/Y or whatever on location, (hell, in most control rooms for that matter!) monitoring is often woefully compromised. A visual pointer of any kind can be useful.

Close micing a piano in stereo, room rumble on spaced pairs that's too low to hear on headphones... I can name plenty of times when you see something before you hear it. the phase scope allows you to pick out harmonic relationships and repetition/noise content alittle better... Is is essential? -no. Is it helpful? -Heck yes! -Hard to clearly convey why, but use one for a while and you'll probably buy one... or at least seriously want to DIY one.

When we bought our first Neve in the mid-1980's, we were shocked to discover that it didn't come with a phase meter. We'd bought two SSLs before that andthey were standard issue on those. We HAD to have one so we specified a custom fitted moving coil Sifam. When we later bought our VR it was a replacement for the V3, and it came with an LED bargraph phase meter. We were transferring over the custom panel from our old V# which had the moving phase coil meter in it, because it also had some custom AMS remotes and a console-mounted return-talkback speaker with grill fitted in. -So voila, we ended up with both LED and moving coil phase meters, which agreed pretty well, though the LED version had an optional 'slow' mode, so we usually left it switched to "slow" to avoid repetition and to get more information at a glance.

We have a few 9098i's here, not all of them have phase meters. We have some SSLs here, they all have phase meters and/or phase scopes in them. It's a little like an oil pressure gauge in a car: nnot essential, but when you get used to having one and know what it'e telling you, it's very reassuring to have one "when the fat hits the shin"!!! :shock:

Keef

 

[SSLtech]

By the way... I thought about DIY-ing an LED phase scope of sorts...

A 20-by-20 matrix of LEDs, with 4 'quadrants' driven by LM391x drivers:

L+R (positive),
L+R (negative),
L-R (positive),
L-R (negative)

Then you just feed in the signal and you should get a dancing dot (only ever one LED illuminated at a time) that -hopefully with the 'persistence of vision' effect- resemble a phase scope image. More out-of-phase is shorter and wider, more mono is taller and narrower. True phase-shifts would show up as geometric loops and patterns.

All you'd do is arrange a vertical array of two back-to-back 391x's to switch a row of 20 transistors to the anodes, and a similar horizontal array of two back-to-back 391x drivers switching 20 transistors to the cathodes of the LED array. Anodes and cathodes all connected together oin respective horizontal or vertical lines. Only one LED at any given time will be illuminated providing the drivers are in dot mode. In bar mode, I think you'd get a rectangle, but I've not thought it out all that far... might work better in high-brightness environments...

Oh yes, and we've all met operators and "engineers" who cannot hear when things are opposing polarity... (beats me.. it turns my head inside out!!!) for those cloth-eared "professionals" who defend themselves with "well, it's not always onvious, you know!!!" a phase meter is a perfect rebuttal: -If you can't hear that it's wrong, there's a meter over there pointing into the red... hopefully your eyes work a little better than your ears!

Keith

 

[rogerroger]

Hello everyone,
this is my first post on this board, and I must say I'm quite a noob concerning electronics, so I hope you'll excuse my sometimes-irrelevant-questions...

I just wanted to know if somebody had tried doing the phasemeter NRGRecordings submitted, and if it works OK, because the 4030 has an input leg (13) up in the air, wich seems a little twisted to me.

thanks in advance,
arthur (yes, I know my moniker is rogerroger, but it's just because arthur was already taken :green: )

 

[nrgrecording]

Doesn't makes much sense with the open input, eh? :wink:

But somehow its the same at the original pcb:
http://www.nrgrecording.de/assets/images/phasemeter_original.jpg

But not a big problem... The pin has to be connected to the to +. I have corrected it.. look here:
http://www.nrgrecording.de/phasemeter_V2.pdf

and here is the schematic:
http://www.nrgrecording.de/assets/images/phasemeter.GIF

 

[rogerroger]

Thanks for the quick answer, NRGRecording,
I'm starting tomorrow
Thanks also for your really nice website. :green: