A commercial station I listen to here in Toronto(when not listening to mine) broadcasts from Oshawa just east of Toronto on AM and FM(same feed).
I listen on AM 'cause the FM only covers locally in Oshawa. They are oldies/classic hits.
Lately the audio on most songs is like listening to a stereo record but with one channel turned off....some of the music is missing. Try listening to Hot Stuff by Donna Summer only hearing bass, drums faintly, and vocal with no guitar! Or Mony Mony by Tommy James& Shondells with just bass and vocal...everything else missing.
I emailed the program director and told him about this and he was surprised to know this....like they never check their on air signal.
Told him it's on all songs some less some more and he said we aren't aware of any problem and it could be something with "phasing" and the usual answer of "no one else has mentioned this"
Maybe someone here with engineering knowledge could know what this could be so I can tell them!
Mark
Sounds like only the left or right channel is making it to the AM airchain. They might've just done some upgrades or moved some equipment around, they just need to make sure the mono-matrix from the board is the one feeding the AM. Heck, it could be their processing gear sums it to mono and somebody accidentally bumped a button. It could also be the station ran C-QUAM and shut it off, either way its their airchain.
I actually worked at an AM station where they tied the right and left channel together and this happened a lot.
I've seen many many stations wired that way, I have no idea why either. It never worked right tied that way and some of those boards had the optional mono outputs!
Tying left and right for mono is not that uncommon. I'll bet there are people on this board that use "Y" adapters for feeding stereo audio to their AM transmitters. Depending on the particular setting this can be perfectly acceptable.
However, they key is phase cancellation. Normally when combining you would connect left + to right +, and Left - to Right -. If you happen to screw this up and do - to + and + to - you're going to get cancellation of any audio that is common between the two channels. One reason it's hard to track down and why it's inconsistent. A song may have music mixed way to the sides of left and right, with a few instruments and vocals mixed to the center (equal on both sides) and it's this common audio that will wine up being cancelled. That's why the effect can seem so different on different songs. Depends how the song is mixed.
Of course I'd actually have to hear it to tell for sure. They could very well have simply lost a side of audio feeding into their audio chain someplace as well.
You have to remember, a large percentage of people won't notice. Of those that do, most won't care. And the small percentage of people who do notice and do care, very few will bother to call the station.
Anyway there's my two cents on that!
TIB
Tim said: "Tying left and right for mono is not that uncommon. I'll bet there are people on this board that use "Y" adapters for feeding stereo audio to their AM transmitters. Depending on the particular setting this can be perfectly acceptable."
Taking it one line at a time... "Tying left and right for mono is not that uncommon."
That is no doubt true, but tying outputs together is bad engineering for reasons that we'll get to in a minute;
"I'll bet there are people on this board that use 'Y' adapters for feeding stereo audio to their AM transmitters."
We are repeating the last statement, using 'Y' adapters as the method to improperly tie two output lines together.
"Depending on the particular setting this can be perfectly acceptable."
False. There is no setting in which tying two output lines together is acceptable.
Outputs are typically low impedance and connecting two of them together cuts the impedance of each in half causing the transistors to heat and distortion to increase. It's like causing standing wave on antenna lines by connecting two transmitter RF outputs together. It is not good practice.
It is easy to make a resistor matching bridge to mix two outputs together in such a way that they are safely isolated from each other just like a good combiner to tie two transmitters into a single antenna.
A "Y" connector can be used to split a mono audio line to feed two mono inputs. That is what "Y" connectors are for.
The AMT3000 and AMT5000 transmitters solve the problem by having on-board L+R mixer circuits so that two stereo lines can be connected and are combined through two 10k resistors into a mono signal.
This is the only time in recorded history that I have disagreed with Tim and it is not a comfortable place to be.
I think Tim nailed it above. In miswiring the + and the - on one of the channels, it will often sound right when listening in stereo. But when the two channels are combined going into the transmitter or you're monitoring on a similarly miswired radio, the cancellation happens.
Most likely right, marosborne, it reminds me of an experience that stations could learn from.
In the 1960s I was brought in by a station to solve a distortion problem with commercials played from a tape cartridge machine. The fix was simple enough involving a resistor matching bridge to correct a mismatch, but because the repair was made while the station was on the air with a morning show in progress, I inadvertantly got one channel of a turntable flipped in polarity before heading home.
The exact problem we're talking about began happening everytime a stereo cut was played on that turntable, but it was undetectable at the station because the DJ heard everything in stereo and had no way to monitor the L+R mix.
Calls began coming in from listeners who noticed that vocals were missing from every other song, and I got a phone call.
The bottom line is, all stereo stations should have the means of monitoring the mix being heard by mono listeners.
Have you ever mistakenly loaded a 4 track tape on a two track machine? I did at a FM station in Albany, Ga.
Both my studio and the stations I worked for had 2-track tape decks so no 4-track tape was anywhere around.
But now on the subject of "mistakes over the air" I will tell you one I made that could have turned out worse.
The studio of an FM station was temporailly located up on top of a building by the tower while the offices were 10-miles away, so I was a lone operator on a weekday morning running music tapes with a live commercial every ten minutes.
Being a "professional", I knew how to take a 10-minute nap and pop up just in time to sight-read a spot. Usually it was the same copy, but one day the gas company had a new script that I hadn't seen.
At the middle of the spot I read... "And the new Laclede Gas Range has an automatic cock timer that.... an automatic clock timer that turns the oven off and on..."
Somehow I made it to the end of the spot without cracking up. The program director heard it in her car and said she almost veered off the road.
Now that's funny. In my case I reorded a 1 hour show and I think is was on a 3600 foot roll of tape running at 7.5 ips. Anyway I had recorded a portion of the show on the flip side of the tape. All went well until the flip side started coming over the 2 track head and suddenly things were playing fowards and backwards at the same time. To save my ass I found an "All Things Must Pass" album on a QRK turntable and I cued up "Thanks for the Pepperoni" song for the remainder of the program. True Story at then station WWCW in Agony, Ga.