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29 MARCH 2017

written by Mike

SOUND ADVICE

ON MIX FORMATS

 

When we think about the sound, we tend to see it as music in your headphones and movies on your laptop. Maybe a surround sound set up at home if you are a grown up. It’s only when you start to dig more into the world of sound engineering you will discover there is a lot more to standard format and mixes.

Today I will share with you an advice and overviews of the most popular formats, mixes and mix elements.

It is important to recognise them and why we use one over another. It’s is only a surface scratch. The area of your expertise and choice of your focus will require learning more about some formats, and the others may be useless to you.

But like with everything else it is good to know the fundamentals, so you have something to talk about with other audio nerds. Excuse me, audio engineers.

Ok, so where is this stuff used?

Everywhere. I mean TV, radio, cinema, games, Internet and everything in between. And the best thing is, every platform requires different formats and conversion.

Fun!

No, not really. It requires a lot of technical knowledge and a lot of work.

Let’s start with the basics.

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Mono

It is one signal. When you record your voice with a microphone, it’s a mono signal.

You can pan it (move it) to the left or the right, but it’s still going to be just one signal. If you duplicate it and pan one to the left and other to the right it’s not going to make it stereo, it will only make it louder (by about 3dB, that is double sound intensity).

So remember while a mono signal can be fed through a pair of headphones speakers it won’t make it stereo. It is still the same one signal.

Stereo

Stereo means having two input signals. For example, if you are recording a guitar with two microphones it will be stereo. One signal goes to the left, the other to the right. It is only the simplest description because the subject of stereophonic sound is very deep.

For example, there is a difference between stereo and a true stereo that can apply to convoluted reverbs. In true stereo, two input signals are split into four and spread to L/R outputs.

There can be other types such as mono to stereo, joint stereo, intensity stereo, mid/side stereo.

For know let’s keep it simple. Two input signals – two output signals. Stereo.

LtRt

LtRt meaning Left Total/Right Total is another two-track element with Left and Right audio but encoded with Dolby Surround matrix.

What does it mean?

In normal Stereo, you got two outputs – left and right. We call that mix Lo/Ro. In Lt/Rt, you have four outputs – L C R S (left,center, right, mono surround).

Four tracks are “downmixed” or encoded into two-track (left and right), but it can be played back as mono, stereo or LCRS. You will need special software plugins or dedicated hardware to encode/decode this mix.

It’s not often used, but clients still ask for it.

Why?

Some old venues that can’t handle standard 5.1 may need it, airline play and TV could use it too.

R128 EBU

R128 is the latest European Broadcasting Union Recommendation for volume and peak levels. These we use for TV broadcast. In postproduction, you may be asked to produce both 5.1 R128 and 2.0 R128 mixes, both set to standardised rules.

What rules?

LUFS, which is relative Full-Scale loudness, must be set to -23dB (with +/- 1dB of margin) with peak set up to -10dB. For feature films, a peak is set to -3dB. ViSLM is a great tool to measure and correct these settings.

We build R128 mixes from separate audio stems.

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5.1

5.1 is now a common name for surround sound. The signal is split into six channels L C R Ls Rs LFE (left, center, right, left surround, right surround, sub) and it is the most common set up in home cinemas.

Most DVD and Blu-Ray systems will decode TV broadcast, clips from YouTube or audio from your phone into surround. But it is only when you listen to true surround mix that you can appreciate the art of it.

Games and Blu-Ray movies will always have a true surround mix, and that’s why they sound better than a TV broadcast or streamed shows. There is much less compression on these disks.

7.1

7.1 is another type of surround sound. The difference between 5.1 and 7.1 is extra two channels of audio. The signal is split into L C R Ls Rs Lsr Rsr LFE (left, center, right, left surround, right surround, left rear surround, right rear surround, sub).

7.1 mixes are much less popular than 5.1 mixes and only in selected countries movies get a 7.1 cinema release. It depends on cinema sound setup.

5.1 mix can derive from 7.1 mixes and that is what mixers still do on most dubbing stages.

Atmos

Atmos is the newest format from Dolby. It is still unknown to the general public and only around 2000 cinemas in the world are capable of playing Atmos mix in full scale.

What is it?

It’s quite difficult to explain in words; you need to experience a demo or a movie mixed in Atmos to understand the idea behind this new system. Atmos system divides mix into objects. It has up to 128 separate channels that the system sends to 64 speakers.

I am only familiar with Atmos mixes for movies so take my explanation of the system as only a small part of the technology.

The way the industry leans towards is to mix movies in Atmos and then derive everything else from it. That means 7.1/5.1/stereo and everything in between will be a “downmix” from Atmos.

Some mixers still hesitate and prefer to mix in 7.1 and only then do a quick Atmos job. It is quite an expensive venture and not as effective. Movies you will watch in Atmos will have sound effects flying all around you, rain coming from above, shouts from the left, explosions from behind.

It is quite something. I may write an article dedicated just to Atmos.

For now, just remember – speakers all around you mean Atmos.

Binaural

Binaural recording gives you the sense of being “in the room”.

What does it mean and how you can achieve it?

And how do you experience it?

Let’s start with the last. Binaural is a headphone mix. I mean you can sort of experience it with surround sound, but headphones are the way to go.

Imagine a band standing in the circle and you being inside of it. That’s what binaural is. It gives you the sense of sounds around you, moving as they pass you.

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