"Mono compatibility" for broadcast-- REALLY?

[sonare]

Recently a friend called in a panic because a client wanted him to record a concert and the local NPR station had said it had to be "mono compatible." Back in the day that phrase usually meant to record with a coincident cardioid pair.

This got me to thinking about the majority of the classical CDs that are broadcast, and that most of those were most certainly NOT done with a coincident cardioid pair for mains. Add to this the ubiquitous Orban device (or something similar) at the transmitter that does all sorts of things, including (hopefully) gentle compression and peak limiting that the restrictions of broadcast impose-- such as not exceeding 100% modulation but yet being easily heard in soft sections.

The purpose of this thread is to ask how many of you do anything different when told it will be broadcast, as well as ask the knowledgeable what the Orban does to LF to make sure the signal is "mono compatible." I can say that I always aim for the best sound (which encompasses phase issues) regardless of main mic technique.

Finally, you are welcome to guess what percentage of listeners actually do so on a mono radio, and if such a device could convey lack of LF.


Rich

[Bob Olhsson]

All broadcast processors and the FM stereo transmission system assume that all source material will be mono compatible. When receivers don't get a strong signal, they switch to mono. Some do this gradually depending on the amount of interference. I'd just check mono to make sure there isn't a train wreck. If there is, you need to move some mikes or do something else to solve the problem.

[mixedupsteve]

I usually check a mix by summing to mono just as a final check but not for broadcast.
I would guess that a great deal of NPR broadcasts get listened to on mono table radios. Say 35%

[aof21]

I've worked at a few radio stations and do radio production now for several. One of the popular radio sound effects packages we use has stereo spreading on pretty much every effect. These are some of the most widely used FX on top 40 radio in America right now. Most of these are not mono-compatible in the sense that if you check them in mono there is a drastic change in the volume of them. However, this just means they'll sound slightly different in mono, not that they totally disappear.

In a different situation I used to work at a college radio station where we would play some unmastered local artists CDs. One of the best stories was when someone called us up and said, you played my song, but the hook was missing! We checked it and what had happened was that the vocals and scratches (this was a hip hop thing) in the hook were so completely out of phase that whatever the broadcast processor did to them, it made them completely disappear!

I'm probably going to butcher this explanation a bit, but my understanding is that a lot of the broadcast processors (made by Orban, Aphex and such) do something like mix a little of the side channels (L/R) into a mono signal, then mix that back out to a stereo mix, but now the left channel and the right channel both have a little of the other channel mixed in. So essentially it allows a station to broadcast something that is "stereo" but there is some kind of summing to mono that goes on to insure that people will hear what's in both channels. I might be very off on this so someone please correct me if possible, I'd like to learn more. There is a chapter at the end of Bob Katz book that explains it as well.

I think the bottom line is this. Whatever you would normally do in mixing is what you also need to do for radio, make sure you don't have a lot of material out of phase, because if stuff is too out of phase it can freak out an air chain processor and turn your recording into something really weird and different sounding. It's actually quite disturbing how drastically the air-chain processors flatten the sound in a dynamics, frequency and stereo field sense. That's why proper mastering is so important to make sure that it sounds the best it possibly can and doesn't have any weird anamolies that will stick out once it is processed in an unpredictable way by the broadcaster's air chain processing.

[Teddy Ray]

Originally Posted by mixedupsteve

I usually check a mix by summing to mono just as a final check but not for broadcast.
I would guess that a great deal of NPR broadcasts get listened to on mono table radios. Say 35%

I have a Magnum Dynalab Tuner

that has a mono/stereo switch...anyway, ive had mine permanently modded for mono only. I prefer radio that way. NPR is one of the few things on the radio that I care about anymore.

Most everyone I know that listens to NPR does so in a car.

[cooker]

I check frequently while mixing. There's 1-2 variable phase plug-in tools out there so you can fix stuff when needed.

Anyway, I didn't care much before but after I realized most stuff I listen is good when mono so I decided to spare time on this while mixing. Interesting, the stereo sounds better (more balanced sort of way) when mono compatible.

I'm not sure why but my guess is the room factor (listening environment) gets more eliminated, but this is just my guess.

[Jim vanBergen]

I check for mono compatibility several times during soundcheck and record, and I watch an X/Y (lissajous) phase scope religiously.

It is a basic standard, nothing difficult to do, (much like parallel compression) and a good practice to perfect, especially once you move on to 5.1 and 7.1 mixing.

JvB

[mixedupsteve]

I use Ozone. It has a button for mono and a phase scope. Very handy.

[0VU]

The majority of my work (80% or more) is for FM radio and some TV broadcast and I always try to maintain reasonable mono compatibility for various reasons, including:

Huge numbers of people listen on mono FM radios, often small ones in their kitchens, gardens, workshops, etc.. With small mono speakers they have little enough LF already, without the recording losing what it has when collapsed to mono.

People living in marginal reception areas often have only mono reception.

As people listening in cars pass through areas of marginal reception, their tuners often switch between stereo and mono to preserve what they can of the signal quality. If the recording is badly decorrelated the recieved sound changes dramatically as the reception mode changes (as can the level).

Non mono-compatible stereo recordings generally sound poorly balanced, thin and nasty in mono whereas I've yet to hear a decent, mono compatible stereo recording that didn't just sound more enveloping in stereo. One of the broadcast people who influenced me greatly in the early part of my career always said that good stereo should sound exactly like good mono, only wider. So the people listening on good quality, well set up stereo hi-fi tuners, with good antennae on decent audio systems in their listening rooms get good stereo, and the (significant numbers) of less fortunate/less discriminating listeners get something more listenable than might otherwise be the case.

People who listen on portable 'stereo' CD/radio/cassette combo boxes or who (like some of my older relatives!) think that their 'stereo system' looks nicer with the speakers next to each other or set up 12" apart, either side of their micro systems, get rotten sound on non mono compatible recordings.

Once I've established that all the pans are correct and the stereo image is as I want it, I usually monitor broadcast (and many non broadcast) recordings mostly in mono to check balance and I don't want to loose the LF if I can help it. (I find it useful, and in many cases easier, to check balances, particularly between soloists and accompaniment, or everything in relation to room sound, by monitoring at low level, in mono, on a single speaker. This is especially true in many temporary 'control room' setups with dreadfully unbalanced acousics and sometimes excessive reverb which are much less of a problem using a single, relatively quiet mono source than with stereo, higher level monitoring. I do flip back to stereo from time to time to check that things aren't going wrong.)


As for using crossed pairs, it's something I rarely do, except for a some occasional Blumlein, and even then I prefer MS. If I want a co-incident pair it's usually MS, for all the normal advantages. Mostly, however, I use near co-incident or spaced techniques, either pairs or Decca Tree and it's quite normal for most or all of any other mics I put out to be omni or subcardioid, perhaps with the odd fig-8 to take care of situations needing extra separation. Though, obviously, that can vary greatly from job to job.

[Larry Elliott]

Originally Posted by 0VU

Once I've established that all the pans are correct and the stereo image is as I want it, I usually monitor broadcast (and many non broadcast) recordings mostly in mono to check balance and I don't want to loose the LF if I can help it. (I find it useful, and in many cases easier, to check balances, particularly between soloists and accompaniment, or everything in relation to room sound, by monitoring at low level, in mono, on a single speaker. This is especially true in many temporary 'control room' setups with dreadfully unbalanced acousics and sometimes excessive reverb which are much less of a problem using a single, relatively quiet mono source than with stereo, higher level monitoring. I do flip back to stereo from time to time to check that things aren't going wrong.)

In this situation do you use a single loudspeaker or two with the same information fed to each?

Thank you

Larry

[0VU]

Originally Posted by Larry Elliott

In this situation do you use a single loudspeaker or two with the same information fed to each?

Ideally, a single speaker as this helps take out some problems caused by using two speakers in an unbalanced acoustic.

I either take along an extra speaker specifically for this, or use the Cut L, Cut R, Mono, Dim buttons on the console to set it up, or I have some consoles and a monitor controller which have a 'Mono on A' function which sends mono to only the left speaker instead of both.

Whether or not I take an extra speaker depends upon things like what main monitors I'm using, the nature or the 'control room' (if known), etc..

[Ozpeter]

If using a PC and you lack any other means of phase display, KVR: UKM Gonio - Virtual Effect has a perfectly good free one.

[Plush]

I do not do anything special to ensure mono compatibility. I have not yet had a complaint. I work for the largest classical radio station/network in America.

[huub]

Whenever my phase correlation meter goes crazy, and also randomy, I push the mono button... If things don't sound too crazy (which is always really) I'm happy..

Interestingly, for 5.1, the mono downmix is pretty relevant really (called HF mode I think, it's a downmix for modulated hf 'analog cable' signal..

[d_fu]

Originally Posted by huub

Whenever my phase correlation meter goes crazy, and also randomy, I push the mono button... If things don't sound too crazy (which is always really) I'm happy..

That's about as much as I do, but then, my recordings don't usually get brodcast...

[Teddy Ray]

Originally Posted by Plush

I do not do anything special to ensure mono compatibility. I have not yet had a complaint. I work for the largest classical radio station/network in America.

Yes sir, but you came up in at an earlier time, and had good people to learn from, so what comes naturally to you or what you do out of habit/experience is most certainly compatible anyway.. for us new folk that dont have access to good teachers, doing things like checking for mono-translation helps the end result.

[Don S]

Originally Posted by Plush

I do not do anything special to ensure mono compatibility. I have not yet had a complaint. I work for the largest classical radio station/network in America.

A downsized NPR engineer here. I've mixed many shows and mono compatibility was never brought up or required. Occasionally we would have problems with stereo mixes. Inexperienced engineers or reporters would put files in our "ready for air" folder completely out of phase due to M-S decoding problems. By the time we found it there would no time to do anything about it.

[panatrope]

I have a badge on the wall in front of me that says: "Bring back Mono" ...

I did most of my early live broadcasting in mono (in good old Ancient Modulation), even though some of the recordings were made in stereo. So mono compatibility was a big issue. If you are making music, you might want your music played accurately on AM stations, so get it right. (Although in some areas 'music' and 'AM' may be an oxymoron.) A lot of portab;e FM radios only have a single speaker. (Most listening now is probably done on portable devices using headphones.)

I now do a lot of work recording for the local classical station. One of their most effective promotions is for the Kloss Model One small radio receiver. This receives FM in stereo (for the headphones) but only has a single speaker ie., mono. We have sold so many that I recommend that it be used as the reference 'check' speaker for our mix - as there is more likelihood of our programs being listened to on this type of receiver than any other particular type.

So check your mix in mono. Apart from micing techniques that give a nice spacy sound in stereo but terrible in mono, there may be errors such as faulty mic or patch cables that reverse polarity, incorrect setting of multi-pattern stereo mics, getting the M and S mics reversed that still sound musically OK when checked in stereo will sound bad in mono.

It is always a good idea when mixing to stereo to have some metering such as a correlationmeter or goniometer display - phase or polarity errors usually appear quickly - important if you are doing a live broadcast. If all you have is a pair of stereo VU meters, arrange to be able to switch them so they can also monitor sum and difference. If the difference level is consistently higher than the sum (mono) level, you will have compatibility problems.

Monitoring in mono - most times just sending the mono signal to both speakers is fine. The BBC is fairly pedantic about its monitoring (particularly on the classical network) and tends to run its speakers at a fixed level. Monitoring control then comprises three buttons - mute, dim and mono, which I believe is set to use the left speaker only.

[fifthcircle]

IME, the mono compatible requirement basically means it can't suck when a mono fold happens. You can get away with a heck of a lot and have it still sound good in mono. However, if you get serious phase issues, you'll have mono sum issues.

What it pretty much comes down to is that if you can make a really good recording that is mostly phase coherent, you'll be fine on the radio. Sometimes, it takes as little effort as just panning your mics either Left, Right or Center. If it works hard-panned, it will work on radio.

--Ben

[7rojo7]

good recordings don't sound bad anywhere