Stereo Processing - Twice as nice?

Stereo Processing

I’d like to talk a little bit about stereo processing and mastering.

So what does it mean, ‘stereo processing’?

Maybe the place to start is to talk about what does it mean to think about stereo – there are really two different ways of thinking about stereo. One is left channel / right channel. You have two mono channels that are feeding two channels in an amplifier, two speakers, and the arrival time coming out of one speaker or the other or both at once will determine the perceived direction of any given sound. If you delay one speaker a little bit, everything will sound as if it is coming from the other speaker because of the precedence effect, or the Haas effect as we know it. So that’s one way of thinking about it – as dual mono.

The second way of thinking about it is something called M/S or Mid-Side processing. It is a style of processing audio that’s coming a little bit more into vogue in some plug-ins, compressors, equalizers and analog equipment that is being introduced to the market over the last several years. Going way back, it is best known as a microphone pickup technique.

The principle of M/S, or Mid-Side is to think about everything that’s coming from both speakers at one (that’s common to both channels) as being one component of the sound and everything that’s different, that’s arriving at a different time from one speaker or the other, or the ‘difference channel’ as being the other component of the sound. This is sometimes known as ‘A minus B’. if you want to listen to the difference signal in a mix or a recording, you can take the two channels in a recording, pan them both to mono, flip one of them out of phase and what you end up hearing is the ‘difference signal’ – everything that’s not common to both channels in a recording.

So that’s a different way of thinking about the stereo field and the way that we thinking about processing stereo – what’s important, what’s interesting, what’s meaningful about this?

If you think about it, when you are listening to two speakers, in order to determine direction you are relying very heavily on this concept of phase or arrival time shall we say. If something shifts in the arrival time between two speakers then suddenly you’ll have a very very different sense of its location. If we’re processing the left channel and the right channel separately and we introduce an equalizer that’s not a linear phase equalizer for instance, there’s a strong possibility that that instrument or that part of the spectrum is going to change in it’s perspective in the stereo image. If that’s what’s desired – great – maybe that’s a desirable effect. But more often than not, we want to do the same thing to both channels at the same time in order to keep the phase coherency between the two channels and maintain that sense of stereo image. What’s important about stereo image is not just the localization of an instrument – not just that the trumpet is coming from right field - but also that the integrity of the reverb stays the same, that the width of the stereo field and the sense of openness and space and top end remains the same as what was present in the mix when it came into the mastering studio.

M/S Paradigm

Processing in the mid-side paradigm has a similar kind of concern about it. In other words if you change the arrival time, the phase relationship between the mid and the side channel, you are likely to drastically change the sense of space in a recording. If you exaggerate the side component too much, you are also likely to find that everything that was in the center of the mix might begin to recede for the listener. I think most people would agree that the stuff that appears in the center of the stereo image is very often the most important stuff. For a Pop mix, it’s usually the kick drum, the snare drum, the vocal, the bass – the main players in a mix. So you have to be careful about how much you change things in the mid channel and the side channel with respect to each other.

What to watch for with stereo processing

As you start to think about mid-side, it’s important to note that there some other arenas of what happens to audio that is playing in the M/S sandbox if you will - where they become important.

The first thing I want to point to is when you are using a stereo compressor. If you are feeding the left channel and the right channel separately into two sides of a stereo compressor and you allow the detector circuit for each side to behave independently, you could end up with some very strange behavior when you are listening to the output of the speakers (listening to a stereo mix) when for instance, the drummer hits a rack tom that appears in one speaker that jumps out of the mix a little bit, one channel of the compressor might be compressing heavily whereas the other doesn’t compress hardly at all and the whole stereo image can begin to steer in one direction or another. So most of the time when we are compressing a stereo mix, we’ll work in a mode where the two channels are linked together and the compressor is really paying attention primarily to the mid component of a mix and not so much to the sides.

How codecs affect stereo processing

In a similar sense, MP3 encoding is based on the idea that you want to try to do as little processing as possible to the most important part of the signal, namely the mid, the thing that is common to both signals and throw away as much of the information that is involved in the quote “less important part of the signal” namely low level signals, out of phase signals, very high frequency, very low frequency signals that are out of phase and so if you start to create a mix where you exaggerate the side information and de-accentuate the center channel, when you pass this audio through an MP3 encoder you may find that you are hearing a much more pronounced effect from the MP3 encoder on your mix.

So there again, you want to be careful about exaggerating the side channel too much, exaggerating the sense of space too much because given that we are all having to deliver things with lossy codecs (MP3, AAC), you may end up with some unintended consequences of your processing.

Reverb and Mastering

Reverb

Today, I’d like to talk a little bit about using reverb in mastering.

The applications for reverb in mastering are in some cases I think quite obvious, but in other cases a little bit less so and some of you may be surprised to learn that reverb comes into play in mastering at all.

Application One – Reverb Tails

The first one is using reverb to lengthen the tail of a song that’s been cut off. One of my pet peeves is that an overeager engineer, or artist or producer will decide that they want to save a little bit of time in the mastering studio and cut the very beginning or the very ending to a song closely so that you don’t have to worry about doing that in the mastering studio. In doing so, they think they’re going to save themselves money in the mastering session, but invariably what happens is that they cut the beginning too close or they cut off something at the very end because their studio is noisy or they aren’t listening carefully and suddenly you end up with a song where you wish the end of the piece could go on another couple of seconds. Or there might be a noise at the end of a mix and you have to pull a fade on the tail to get a ringing note down before the noise comes in and causes an interruption in the attention of the listener. So in any case, we might use reverb to extend the tail and in this case it’s a pretty simple think to apply reverb just to the very end, have it gradually rise as the last note decays and try and create some sort of sense of a natural extension to the last note for as long as need be.

Application Two – Acoustic Space

The second place that reverb comes into play in mastering is when you are trying to match the sound of two different recordings that are coming from two different acoustic spaces – one might be dry and one might be ambient – that are going to be included in a single album’s worth of material. This comes into play most often when I’m working with something that comes from various orchestras from around the world. I’ve received recordings made in Seattle, Bratislava, Warsaw and Prague and each engineering crew has their own aesthetic about how much reverb they like to allow to creep in, or ambience they like to have creep in to the sound of the recording. In some cases they are bound by the dimensions of the space that the orchestra is playing in.

So if I’m doing a record by a single composer and their works and it’s recording in multiple places, I might apply some reverb to some of the recordings to bring them into a similar sonic universe when going from one to the next.

Application Three – Creating A Sense Of Depth

The third instance where reverb might come into play in mastering is when I want to be able to create a little bit of a sense of depth in a recording. There are those moments where I will have done everything that I can think of to do that seems to be making a recording sound better with EQ, with compression, where I just want a very tiny sense of warmth and sort of a widening and deepening of the soundstage. And more EQ is just making it worse, more compression is just making it worse and I’ll try adding a hint of a very short, not very bright bit if reverb to the sound of the recording.

My recipe is usually rolling off the top end of the reverb, setting the roll-off somewhere around 2.5 or 3 kHz, having a decay of about 2/3 of a second and just a little touch of it – sometimes that gives me just that sense of depth that I’m after in a very natural way, in a way that an EQ or a compressor is not able to do.

You have to be careful, because if you add reverb to a heavy metal tune, a punk rock tune or something that really needs to maintain it’s immediacy and edge, reverb will soften the general sense of the program usually. but It can come in handy.

Another record we are proud of...

What a joy to be able to help bring so much expression, joy and, well, music into the world.

Here's a review of just one example of a project we are proud to be a part of. Powerhouse modern big band with some inspired performing....and dynamics to boot!

http://www.jazmuzic.com/2011/12/cd-review-new-world-jazz-composers.html

Another vote for good sound....

This piece gives some nice ammunition to those of us who believe that good sound is an important part of musical expression, and that regular ole people, even the mp3 generation (!) can discern differences in sound quality....and they might even prefer higher resolution.

http://tinyurl.com/7t7s4m3

Provides just a tiny hit of job security!

As I have said many times, I don't have much of a gripe about mp3....or cassette or whatever, so long as it is where it belongs: in the domain of the consumer. In fact mp3 represents a leap forward for people in many parts of the globe.

Where I DO have a problem with it is when it is confused with professional production tools. That is a non-starter in every way. It is tough soetimes to distinguish between a professional tool and a hobbyist toy when they both reside on the same platform; laptop, desktop or tablet. Indeed there is a world of difference however!

But really what IS loud

For years now my brethren in the mastering profession have been jumping up and down in defense of music and in self-defense, trying to raise flags about what is happening to music during the so-called Loudness War.

Indeed, the way that the RMS level have been creeping higher and higher as the dsp tools we have are better and better at hiding the distortions of limiting and compression, has caused immeasurable harm to the presentation of recorded music. It permeates all genres and affects pretty much ALL artists. It's frightening to think that we adapt to it, assimilate the new sound and begin to become numb to the effects.

There are developments on the horizon for creating a level playing field in the presentation and playback of music to the consumer that hold some hope that we might return to what Mastering folks might call 'sanity'....

but....and....however...

I think that the story that has been told thus far about the loudness war, how it is motivated by the fear of A&R , PD's in radio and other decision makers might reject an artist, only tells one part of the story. I think there is something significant that is escaping everyone's attention. Perhaps it is being 'masked' the the gross issues of RMS volume, but beneath the surface I think part of what is happening is that the craft of producing recorded sound is suffering. I think the art of making a good, well balanced recording is eroding and I think that the real ART of making a truly loud record is being lost.

A couple of years ago I gave a presentation to my fellow faculty at Berklee entitled 'What IS Loud?'. I sought to deconstruct the idea of loud. Focused on frequency distribution, the art of arrangement in music, the art of dynamic control in mixing and it really looks like making a truly loud recording involves time, skill and even, yes, nuance.

I hope to slowly unfold this topic....especially if we end up with the new BS1770 standards for playback reference, I think it will become clear what loud and GOOD mean again.

Metadata, ISRC, UP and QC

What is metadata?

Any information that is included within a program, whether it is for a download or creating a disc, that is not the program itself. It is embedded within the digital file (as a download or when burned to disc). Examples are track IDs, start and stop IDs, ISRCs, UPCs, and CD Text information. One of the things that the mastering engineer is responsible for is understanding what these are and including all this information in a master.

What is an ISRC?

It stands for International Standard Recording Code. It is a number that is allocated to any publisher (record label, artist, or anybody that is owns a catalogue of music). It is registered in the USA with the RIAA (Recording Industry Association of America) and in Europe with GEMA (a performance rights organisation) . The code is a unique identifier that gets attached to every single piece of music (each song within a record would have its own ISRC code). Any time that the music is played over the air, downloaded or streamed, the identifier is logged. This is vital in the payment process .

http://www.usisrc.org/

What is a UPC?

It stands for Universal Product Code. Is a number assigned to a product. Traditionally it has been a physical item, such as a cereal box in a grocery store, which has a bar code (and correlating number) to scan at the checkout to identify what that product is. The same is true of CDs or DVDs. But they are also used to track downloads in some cases, so you should register and include it in your product.

What is QC?

This is what is known as Quality Check. Mastering is the final process before distribution. As a result, it is the mastering engineer’s job to make sure that there are absolutely no flaws in the program (a dropout or a click for example). The mastering engineer should give the client assurance that there is no problem with the audio.

On Stereo-Imaging

Stereo-imaging tools are often included in DIY mastering packages or equalisers with stereo spreading facilities (most commonly offering some kind of mid-side processing options), so it is important to acknowledge their purpose and their limits.

As with many of the specialist tools we have for processing audio, they are great at solving specific problems. If you have something mono or largely in mono, for example, and you need to try and widen it, you can add reverb or perhaps exaggerate the little stereo information that already exists in the track.

But what exactly is the ‘stereo information’?

Well, it has to do with the relationship between the ‘out-of-phase’ information, and the ‘in-phase’ information. Anything that is in-phase happens at exactly the same time in both channels, and that information will appear to be centered. If anything is slightly delayed off to one side or the other, compared to the center of the image, it is ‘out-of-phase’ and is one of the things that creates a stereo sense of spread.

So when you are mixing, you are using pan pots, delays and reverbs (etc) to create a stereo image of individual elements within an overall stereo mix. However, when you go in during mastering and increase the out-of-phase component, you are changing the relationship between the out-of-phase and in-phase parts of the signal of the entire mix. You therefore are able to radically change the sense of the stereo image and the placement of each individual instrument in a song, which can be very dangerous if not treated with care. And although you may increase the perceived wideness, this is at the expense of the in-phase components in the song. That is to say, the elements that are dead-center, which also tend to be the most important elements of most productions – vocals, snare, kick, bass – are weakened.

So sometimes – in its various forms – stereo-imaging can be used to good effect. However, one should err on the side of caution.