I'm still thinking about when I would want a correlation meter. The scenarios are few.
In broadcast about the most obvious application is in machine room/content ingest applications where you occasionally get stereo content delivered with the polarity flipped on one channel. I think it makes sense in a Wholer-type monitor panel. In that situation "negative correlation" would need to be bright red.
Now that I think about it, sitting behind a console in a remote truck doing football I'm not sure how much a correlation meter would tell me. If it's mono I think I might be able to hear that.
For classical/acoustic recording/broadcast, particularly M/S, it might be useful.
But for live rock-n-roll I'm hard-pressed to figure out why I'd need one. In mastering I'd want a scope display.
An absolute polarity meter would be very useful for recording and mastering.
SSL Phase Meter Schematic
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mediatechnology
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Re: SSL Phase Meter Schematic
Absolute polarity meter? I am not sure how to do this in a receive only environment. We can make assumptions about acoustic instruments wrt typical waveform asymmetry but I don't feel lucky to come up with a reasonable algorithm.
JR
JR
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mediatechnology
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Re: SSL Phase Meter Schematic
I did it with log amps and ratios. I don't think it would be too hard in DSP.
At some point in the chain you have to define the electrical polarity from the correct acoustic polarity using a measurement mic to define "right-side up" as pressure. If the speaker drive is "waveform positive" and the cone goes out you're in good shape for monitoring.
You can check the acoustic polarity of virtually any microphone by talking into it and monitoring it on the 'scope. Most any vowel will be heavy-positive. "E" is my favorite vowel.
I see this as a recording/mastering thing to make sure as many waveform asymmetric elements in the mix are pressure-generating or positive-heavy to the master. After that all bets are off of course but at least all the elements are "wrong" together.
At some point in the chain you have to define the electrical polarity from the correct acoustic polarity using a measurement mic to define "right-side up" as pressure. If the speaker drive is "waveform positive" and the cone goes out you're in good shape for monitoring.
You can check the acoustic polarity of virtually any microphone by talking into it and monitoring it on the 'scope. Most any vowel will be heavy-positive. "E" is my favorite vowel.
I see this as a recording/mastering thing to make sure as many waveform asymmetric elements in the mix are pressure-generating or positive-heavy to the master. After that all bets are off of course but at least all the elements are "wrong" together.
Re: SSL Phase Meter Schematic
Interesting... in recording studio they should have pretty good handle on polarity... perhaps downstream feeds?
JR
JR
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mediatechnology
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Re: SSL Phase Meter Schematic
John - Unless they have a 'scope or are working on a DAW I don't know how they would have a visual indication of absolute polarity in the studio.
Re: SSL Phase Meter Schematic
AFAIK studio equipment designers figured out that Absolute Polarity was worth preserving back in the early '80s, so gear made since then should be reliably polarity correct.. DIY or esoteric gear not so much...
Prior to that it was so bad I put a polarity switch on one of my phono preamps to correct for records that could vary from track to track.
JR
Prior to that it was so bad I put a polarity switch on one of my phono preamps to correct for records that could vary from track to track.
JR
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mediatechnology
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Re: SSL Phase Meter Schematic
John - I edit a lot of commercial modern music (head/tail trims, normalization etc.) You'd be surprised at the number of entire mixes, or elements in mixes, that have it upside down on the CD. We may now agree that pin 2 is really hot, but that doesn't solve the problem.
The other day I was listening to a 96 Kbit MP3 smoothjazz.com feed and the sax sounded just awful across multiple cuts. (Sax being a smooth jazz staple
). I had the scope fired up and decided to look directly at the speaker terminals. It was inverted at the + terminal and still - despite processing and compression - very asymmetric. (I know from connecting a battery years ago that + is out on that particular model.) I tried cuts that I knew were right-side up. Still inverted. I decided that the power amp or soundcard were upside down. So I reversed both speaker leads.
I don't know how much of a difference it really made but I do feel better.
EDIT: BTW the soundcard I was using that day had only been in the machine about a week or I may have noticed it sooner. That may be the culprit. It would be instructive to compare it to the other installed soundcard that I previously used for monitoring. That one is now dedicated to measurement.
Seriously though: I've found sax in particular - if upside down - seems to have less "bell" and more "reed." More lip, more squawk and less rounded tones. On that mp3 stream I heard some really "Honky" sax. If I were recording sax I'd sure want to put it on the scope (and check it acoustically) to make sure "up is up" at the ear before I made too many EQ decisions.
Most acoustic instruments (including voice) are better at creating pressure than vacuum. Nature wants recorded music to be rightside up.
The other day I was listening to a 96 Kbit MP3 smoothjazz.com feed and the sax sounded just awful across multiple cuts. (Sax being a smooth jazz staple
). I had the scope fired up and decided to look directly at the speaker terminals. It was inverted at the + terminal and still - despite processing and compression - very asymmetric. (I know from connecting a battery years ago that + is out on that particular model.) I tried cuts that I knew were right-side up. Still inverted. I decided that the power amp or soundcard were upside down. So I reversed both speaker leads. I don't know how much of a difference it really made but I do feel better.
EDIT: BTW the soundcard I was using that day had only been in the machine about a week or I may have noticed it sooner. That may be the culprit. It would be instructive to compare it to the other installed soundcard that I previously used for monitoring. That one is now dedicated to measurement.
Seriously though: I've found sax in particular - if upside down - seems to have less "bell" and more "reed." More lip, more squawk and less rounded tones. On that mp3 stream I heard some really "Honky" sax. If I were recording sax I'd sure want to put it on the scope (and check it acoustically) to make sure "up is up" at the ear before I made too many EQ decisions.
Most acoustic instruments (including voice) are better at creating pressure than vacuum. Nature wants recorded music to be rightside up.