Re: (Long Message Here But Hopefully Informative)
> > What is "mix/minus"?
>
> > BUT if you feed that entire "mix" back into the phone for the
> > caller to hear you get screeching feedback.
There is another reason to use Mix-Minus that you might want to discuss. It is also used for remote broadcasts. This includes remotes done via RPU transmitter, telephone devices such as Comrex Hotline, and Telos ISDN tranceivers. It would also apply to methods such as sattelite, and anyone daring enough to send audio over the internet, but we do not use either of these last two methods.
The problem is one of audio delay - just like you get in a recording studio when someone puts an echo effect on a guitar for instance. The farther away the talent is from the studio, the more delay you get. Yes - the audio signal travels at close to the speed of light through the wires and analog equipment that it passes through, but believe it or not, the human ear can still perceive this as an echo, at what might seem microscopic delay times - on the order of microseconds. On the surface, this may seem ridiculous, but how do you think the human ear and brain can tell what direction a sound is coming from? They determine direction by the tiny delay time between the arrival times of a sound to both ears - a sound coming from your left will arrive to your left ear sooner than it arrives to your right ear.
With analog devices, such as a fully analog studio console, an RPU transmitter, and FM Subcarrier for IFB, the delay is minimal. HOWEVER, with the explosive growth of digital devices in our audio world, the delay times have become much greater - in some cases as long as MANY SECONDS. Digital devices such as Hotlines, ISDN, sattelite, and don't forget CELL PHONES - all have computer chips and analog-to-digital converters that convert the audio of our analog world into the ones & zeros of the digital world. The problem is that this conversion takes time. It can take anywhere from a few hundreths of a second, to many seconds depending on the devices and transmission methods. Our Telos ISDN boxes have about a one-second roundtrip delay when using Layer 3 mode. Our internet audio streams are done on a PC with Windows Media Encoder, and it takes about 8 seconds to be encoded, sent to the internet, then decoded by a listening PC. Yes - EIGHT seconds..!
Ok fine, "why's he saying all this?" you're thinking. This is why: the problem arises when the talent listens to the air signal in his/her headphones. If the talent listens to the air signal, they will hear themselves in delay. In other words, they don't hear themselves immediately - they hear an echo of themselves. And the length of the echo can be anywhere from milliseconds to many seconds depending on the equipment. And this gets CONFUSING. Your talent will start to hesitate, stutter, and sound like a dork on the air because they can't hear themselves correctly. In some cases, they might even stop and drop a nice "is this thing on?" on the air.
If there is a mixer at the remote end, and the remote producer/engineer creates a "local mix" of the program audio & air signal, the effect will vary. What happens is that when the talent is not "potted up" and on the air, they sound normal to themselves in their headphones. BUT the problem starts as soon as they go live on the air, and start hearing themselves from the local mix, as well as through the air feed. Why? Keep reading.
If the equipment at both the remote and studio is all analog (and thus a very short delay time), the talent will hear themselves in their headphones ok, but the audio will sound like it's kind of out of phase, or like they are talking into a milk jug or a bucket. As the distance between the studio and the remote site increases, so does the delay time. Thus the "bucket" gets bigger and the audio more weird sounding. Most of the time, talent can work with this, but you still generally want to avoid it if you can.
If there is ANY digital equipment in the audio path, the delay becomes MUCH GREATER. When I do remotes with ISDN in Layer 3 mode, the delay time is almost ONE SECOND. I do have a mixer at the remote site to create a local mix so they can hear themselves in their headphones, but sometimes the producer back at the station forgets to keep our fader OUT of Audition on the board (yes we do it that way - big cluster, many stations, lots of shared inputs - can't use dedicated MixMinus modules)... This usually results in a fast and heated phone call from myself to the producer back at the station to yell at them about it (again) (Arrghh!)
. Most of the time the talent takes it in stride (with difficulty), but every once in a while it really throws them off.
Another thing to consider when this kind of delay is involved is the queueing of talent with music - or anything really, including commecrials. If the talent likes to hit those song intros and outros like a hammer, it't NOT going to work with a one second delay! They're gonna be stepping all over the songs and their little egos will get hurt, and then they'll probably get all ticked off and start yelling at someone - usually the remote engineer (aka - ME). The talent AND the producer back at the station MUST be aware of the delay and that they have to "run the board loose", not to mention keeping the fader out of audition on the console.
In regards to the simple act of putting a phone caller on the air for a radio talk show, if there was not the problem of screeching feedback, there would still be the problem of the delay. I hear it myself every time I set up an RPU remote and call the studio for a sound check. If I have my cell phone up to my ear, and talk into the mic at the remote, and the producer has the studio speakers turned way up, I can hear myself in the studio speakers back through my cell phone - but with noticeable delay. Now because the RPU is analog, it's signal gets back to the station faster than the audio from my cell phone, which is delayed because of its digital audio converters. This delay isn't excessively long, but if the two signals were put together in a headphone mix, it would be pretty distracting. SO - the point here is that feedback or no, we still need mix-minus for phone callers.
Hope this helps.
Matthew Shea, Radio Engineer
Entercom Communications
WBEN, WTSS, WKSE, WWKB, WGR, WWWS, & WLKK
500 Corporate Parkway, Suite 200
Buffalo, New York, USA
(716)843-0262
