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Phasing phunks

J

johnbasalla

For many years, I remember hearing phasing problems on a few old records when played on the radio. The best known example is/was "Purple Haze" by The Jimi Hendrix Experience. On the stereo FM station, the vocals would almost disappear. I also remember hearing a problem with "Whatcha See Is Whatcha Get" by The Dramatics, an early 1970s R&B hit. In this case, the station was an AM station who were using a satellite service for their music. Half of the music was missing. Have you encountered this? Would the, or an answer have been to play them in mono?
 
I remember that happening with the original CD release of "Creeque Alley" by the Mamas & Papas. We ended up dubbing the cut on a cart while running it thru a phase flipper to fix the problem. This would have been around 1985 or so.
 
Where you run into cancelled audio is when something horribly out of phase in placed in mono. Many FM receivers will blend to mono as they detect lower signal strength. This is what happens if you remember or even actually happen to have an FM receiver with a "local/distant" switch. Putting it in distant forces it to mono. So if the left/right channels are completely phase flipped to 180 degrees (as bad as it can get) everything in the center will more or less cancel. The mathmatical equation is 1 + -1 = 0. That's why vocals will disappear as they're usually recorded in the center, with left and right being equal. I had an oldies station that would run into phasing issues from the source material, and sometimes I could solve it with a Howe Phase Chaser. Phasing is pretty much a dead issue unless you're reproducing from magnetic tape, which almost no one is these days.
 
Have you encountered this?
Click to expand...

How about as recently as a few months ago, and on more than one station in more than one market ! :mad:

What I hear is not so much the classic channels-completely-out-of-phase issue, but channels-not-combining-correctly-into-mono. It's a sound surprisingly similar to an out-phased cart machine, but in this case it is on FM stereo stations verified to be all-digital. I blame a mix of bad sample-rate conversions and just plain crummy MP3 originals.

I also blame radio folks who don't pay any attention to real mono, or honestly just don't really listen to their own station any more. Yeah, the old truism about remembering "clock radio" (mono) listeners may be outdated, but what happens when your listener hits a bit of multipath and the car radio blends to mono on your bazillion-dollar rimshot signal?
 
What you could be noticing is l-r processing employed at some stations, or the stereo enhancement that's present on most digital audio processors. If it's over-the-top it will alter the sound of the mono sum.
 
Low cost audio cards with a single DSP (that's shared between the left & right channel) can cause a phase error. A lot of these on-board sound cards first decode the left channel then the right. That delay results in quite a phase error @ 15 kHz. Have had to educate people can't play something from Media Player into Adobe or TLC on their office PC.
 
As a point of notice, the last receiver I had with a LOCAL - DISTANT switch used it to switch about a 15 dB pad in and out of the front end. On the other hand, the STEREO - MONO switch forced it into mono.
 
I've seen that happen on a brand name, high cost, T1 encoder/decoder. Phase error was frequency dependent. Really made a mess of the FM coverage; mimicked terrible multipath.

boiseengineer said:
Low cost audio cards with a single DSP (that's shared between the left & right channel) can cause a phase error. A lot of these on-board sound cards first decode the left channel then the right. That delay results in quite a phase error @ 15 kHz. Have had to educate people can't play something from Media Player into Adobe or TLC on their office PC.
Click to expand...
 
boiseengineer said:
Low cost audio cards with a single DSP (that's shared between the left & right channel) can cause a phase error. A lot of these on-board sound cards first decode the left channel then the right. That delay results in quite a phase error @ 15 kHz. Have had to educate people can't play something from Media Player into Adobe or TLC on their office PC.
Click to expand...

This can be a problem even in the big leagues.
A number of years ago, at an unnamed major radio station in London, I was demoing an Ariane when I found I could not get a good mono null in the program material. I chased my tail for a few minutes until I looked at the incoming audio itself. Turned out the left and right program audio channels going into their audio processing were not time-balanced, for one reason or another, and generated considerable L-R even in "mono". I told them that, regretfully, I didn't think that installing the Ariane as a matrix processor would be a good idea until they fixed the issue. Not sure if they ever did. :-(

David Reaves
 
I found out (the hard way) some years ago that when changing a Moseley 6000 series STL system from composite to mono, you can get a 90 degre shift by doing the jumpers just a little bit wrong. Really fun to chase down.
 
I accidently flipped one of the shannels on a station I was CEing and got a call from them saying mono listeners could not hear any voice in the spots. As mentioned above the spots laid down the announcer on each channel equally but the music was fed to channels differently in the end the announcer was gone. It sounded fine in stero which was what they monitored in so they never heard the problem. I flipped the line on one side and the problem stopped.

As to the comment that this doesn't happen in the big leagues, Friday I listened to Bubba the Love Sponge run a best of and a whole segment, maybe 20 minutes was inaudable on my mono radio.
 
littlejohn said:
I found out (the hard way) some years ago that when changing a Moseley 6000 series STL system from composite to mono, you can get a 90 degre shift by doing the jumpers just a little bit wrong. Really fun to chase down.
Click to expand...

A 90 degree shift? ???

Not 180?
 
It's been a while, but I think it was in the process of jumping from unbalanced to balanced....but in any event, if you do it just wrong, that's what you get. Sounded equally awful in mono whether you reversed phase on oner input or not.
 
littlejohn said:
It's been a while, but I think it was in the process of jumping from unbalanced to balanced....but in any event, if you do it just wrong, that's what you get. Sounded equally awful in mono whether you reversed phase on oner input or not.
Click to expand...

Wow! Depending on the test gear you had handy, that one could have left you scratching your head.
 
I forget the brand, but about 30 years ago in Denver we tested some STL's that without an O'scope to set up would have up to 180 shift in the mid to high end with normal in the low. It could swing the full 360 over the range 20 HZ to 15Khz. Really sounded crappy. We sent it back.
Bill
 
Re: Phasing phunks-Bilco post

Did you tell the company that the STL sounded lousy? Maybe you got a defective one. How could the sell any of them if they were universally bad?
 
I imagine we would have but that was a long time ago. I recall that they went out of business fairly quickly. To many years ago to remember the name. The good news is that companies that produce products that bad rarely last.
 
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