Monday September 26, 2011
I made a short video about stereoizing an electric guitar recording, which you can see here...
By 'short' I mean it's just a single example based on some work that was sent in to us. There are lots of other ways to do it.
One viewer asked the question, "Can you explain the pros and cons of stereo?"
Well that's a simple question, but does it have a simple answer?
If asked in an elevator (the 'elevator question', like the 'elevator pitch'), I would say that it provides a more enveloping experience than mono, more akin to what we hear all around us in everyday life. So that in a nutshell, or in an elevator, is why it is better. I could say more, but I'd need all day, and a consultancy fee ;-)
But can mono sometimes be better than stereo? Now that's a more interesting question because stereo is pretty much universal. Stereo is also a more recent development than mono. Therefore stereo must automatically be better surely?
Well, not always. Here are a few examples...
I don't only mean the actual Beatles, I mean any record from the early 1960s that follows the philosophy that no effort is spared to get the mono mix absolutely perfect, and the stereo mix - done by the assistant after everyone else has gone home - is run off in a few minutes. Or a couple of hours for a full album. (This has been well-documented for The Beatles, but is also how mixes were made for other artists.)
In those days few potential buyers had stereo equipment, so this made a lot of sense.
So if you rummage around secondhand record stores, boot sales, yard sales and other likely outlets, you can find 1960s albums, and often the same album in mono and stereo versions. I can tell you that some of those mono mixes sound GREAT. If you focus your attention on mixing specifically for mono, then it is amazing how good it can sound.
The loudness war
Let's suppose someone high up in your own personal food chain has asked you to make a mix really loud. How can you get an extra 3 dB without sacrificing even one iota of sound quality?
Let's suppose you made a mix (normalized to 0 dBFS) that had a huge amount of stereo content. So much so that your phase meter bends over backwards much of the time. (If you display a stereo signal on an oscilloscope using the X-Y mode, a mono signal will show as a straight line angled at 45 degrees upwards to the right. A stereo signal will show a similarly angled ellipse. If you increase the stereo content this will tend towards a circle. If you add out-of-phase content, it will lean over to the left. Pure out-of-phase is a straight line angled upwards to the left.)
So you have audio coming out of the speakers on the left and you have audio coming out of the speakers on the right, but there isn't a great deal of correlation between the two.
Now mix the same track, but in mono (normalized to 0 dBFS). Suddenly you will find that the mix, played back on speakers, is 3 dB louder. That's because when two signals that are equal in level but uncorrelated are added together, the sum of the two is 3 dB greater than either signal alone. But when they are fully correlated, as in mono, the sum rises by 6 dB. It's three decibels for free! What's not to like?
In reality, there is always quite a lot of correlation between the two channels of a stereo mix, so the benefit is not the full 3 dB. It's still a reason however for panning bass instruments and kick drum center instead of hard left or right.
Do people still listen on FM radio? Although we can now listen to digital radio via digital radio sets, satellite TV systems, Internet etc., many people have not scrapped their portable AM/FM radio and you will often find one playing in the kitchen of the house. And let us not forget the car! It will be a long time before no car is sold that has FM radio capability.
FM stereo was a great invention. It 'piggy backed' the difference between the two channels onto the mono signal, which is of course the sum of the two channels of a stereo signal. A decoder can easily turn this into left-right stereo while maintaining full compatibility with older mono sets. Genius.
The downside is that the difference signal doesn't have much of a signal-to-noise ratio, therefore if the broadcast signal is weak then the audio will be noisy. On some FM radio sets, you can switch to mono, when you will hear a much less noisy signal. It's a big difference. And most sets will do this automatically when the signal is really weak.
In consequence of this, many people listening while driving will be hearing a mono signal. If your mix doesn't sound good in mono, then hard luck - it either won't get broadcast in the first place, or listeners will desert the station.
You can enjoy great stereo by sitting exactly between a pair of stereo loudspeakers, properly positioned. That is you as an individual. Invite some more people to the party and only a few of them will be well placed to hear stereo as it should be heard. Invite a few more and many of them won't get the stereo experience at all.
If your mix doesn't sound good when there is a whole party-load of people, chatting and downing drinks, then you can't say that it is entirely a good mix, however brilliant it sounds when properly heard in stereo.
In summary, there are situations where mono is unavoidable. And there are many examples of recordings that sound wonderful in mono.
Maybe mono isn't such a bad thing after all.
My question now to Audio Masterclass visitors, does anyone actually prefer mono to stereo?
By David Mellor, Course Director of Audio Masterclass
Monday September 26, 2011