MS Mastering(Letto 107 volte)

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MS MASTERING

The so-called M/S Mastering It involves the execution of some types of processing operations, which can be performed between one encoding operation and another decoding operation of the mix, which transforms its LR matrix (Left-Right) in a M/S matrix (Middle/Side) and vice versa, allowing us to independently filter the central elements (M – Middle) and the lateral ones of the L/R stereo image (S – Side); hence the acronym MS.

To do this, if the convenient plugins for encoding (before the process) and decoding (at the end of the process) operations are not available, it will be necessary to first build a specific and relatively complex audio path on our DAW.

The MS chain

Basically, it's about installing a complete mix track into our mix track. M/S matrix  aimed at alternative audio processing.

It will be composed, in order, of:

1. a M/S encoder, For transform the LR signal into M/S (M/S encoding)
2. a unit of M/S processing, that is to say 2 parallel chains of tonal and dynamic processors in the form of plugins, one of which is dedicated to the processing of the M channel and the other for the S channel
3. a M/S decoder, to transform the M/S signal back into LR during and after processing so that we can monitor and correctly use the result of our manipulations carried out in the M/S domain.

LR to M/S encoding

Starting from our original LR mix, this is the first step to take, which will allow us to break down the LR stereo sound through the application of the following formula:

M (Middle channel) = 1/2 (Left + Right)
that is to say that the Middle channel is obtained by mixing the Left channel with the Right channel at the same volume towards an aux bus, and then attenuating the result by -3dB

S (Side channel) = 1/2 (Left – Right)
that is to say that the Side channel is obtained by mixing the Left channel with the Right channel at the same volume towards an aux bus (the latter however with inverted phase polarity), and then attenuating the result by -3dB

M/S Processing

Between the encoder and the decoder we can install, for each of the M and S channels on the relevant aux bus, a equalizer and a compressor, but possibly also others processors as needed in order to manipulate the audio thus decomposed, before recomposing it via the decoder.

A description of some of the most typical audio manipulations executable by means of theM/S processing is described later in this chapter.

M/S to L/R decoding

At the end of the processing carried out in the domain of the M/S matrix, to reconstitute the program of the LR stereo matrix, which can then be used for further processing and for exporting the master, the following inverse formula must be applied:

L = M + S
that is to say that the Left channel will be obtained by mixing the Middle channel and the Side channel in an aux bus, at the same volume.

R = M – S
that is to say that the Right channel will be obtained by mixing in an aux bus, at the same volume, the Middle channel and the Side channel (the latter after having inverted its phase polarity)

How to set up the matrix  M/S on the Daw

According to the characteristics of the DAW there are three ways to operate. 

Here they are:

1 – If you have a plugin with M/S encoder functions you can do this:

• install it directly on the mix bus insert (track that conveys the entire mix)
• Next, in the insert chain, install the processors to be used for the appropriate manipulations in the M/S environment, making sure that they can be set in dual mono, in order to allow independent adjustments for the two M and S channels.
• at the end of the chain, install a plugin with reverse function of M/S decoder

2 – if you have a plugin with M/S encoder functions but you don't have processors that work in dual mono: 

• Install the M/S encoder directly on the mix track insert
• route the 2 M and S outputs of the plugin to 2 mono buses that you will call M and S
• on these independent M and S buses install the processors to be used for sound manipulation, independently for the 2 M and S channels; 
• channel the mono outputs of the 2 M and S buses into a “stereo” bus, in which you will install the M/S decoder, in order to convert the M/S matrix into an L/R type one

3 – finally, if you don't have the above encoding and decoding plugins, things get a little complicated, because it will be a matter of manually creating the right signal paths and performing some phase polarity inversions, operations indicated below:  

Encoding

1. transport a copy of the original stereo mix, splitting it onto 2 distinct mono tracks (L and R, which we will now call A and B) and keeping the pan-pot of both tracks A and B at the center
2. reduce the volume of the 2 tracks A and B, each by 6 dB, and channel them at the same volume into a mono bus that we will call M (Middle), which will constitute our central channel
3. repeat operation “a”, transporting a second copy of the mix onto 2 other distinct mono tracks (L and R, which we will now call C and D), also in this case keeping the pan-pot of both at the centre
4. invert the phase polarity of track D only (R), by means of a phase inverter (which is sometimes available on the track's controls) or by means of a specific plugin equipped with a polarity inversion switch, to be installed on the track (this switch is often available in eq plugins)
5. decrease the volume of the 2 tracks C and D, each by 6 dB, and channel them into a mono bus that we will call S (i.e. Side), which will constitute our bilateral channel
6. by means of these operations you will have obtained two separate mono buses with the respective M and S channels,

Processing

1. on each of the aforementioned M and S channels you can install a chain of processors, as needed and independently for each channel
2. After processing, however, we will have to restore the L and R stereo image so that we can monitor the processing operations and use the sound obtained in the M/S domain in a normal LR matrix.

Decoding

1. route the outputs of the two M and S buses into another mono bus and you will get the L channel
2. route other parallel outputs of the same M and S buses (if you don't have them you can use the bus aux sends) into two other mono buses and invert the phase of the S bus only
3. Now combine the outputs of the M and S buses (the latter with the phase inverted, therefore) into a single mono bus, and you will have obtained the R channel.
4. finally, channel the L and R channels thus obtained into a new stereo bus that we will finally call L -R, and that's it.

This is a complex operation, but not difficult to perform if you follow the instructions step by step. 

Let us now analyze what advantages we can obtain by processing the channels of the M/S Matrix with equalizers, compressors and volume controls inserted between the encoder and the decoder.

Mastering operations with the M/S matrix

Acting independently and appropriately on the volumes of M and S channels we will be able to obtain some improvements, which would not be achievable without this technique.

Let's look at some of the most typical ones.

Regulating the relationship between spatiality and presence

• By varying the ratio of volume between the central and bilateral channels, you will obtain a general effect of greater presence and “concreteness” (by raising the volume of the central M channel) or more spaced (by raising the volume of the lateral S channel).

Straightening an unbalanced stereo image

• By changing the setting of balance of the individual L and R channels placed in input on the S channel (during encoding)

Increase presence and definition without taking away spatiality

1. With theequalizer High Shelf will be possible to make the “rooms” wider and brighter simply by increasing the clear frequencies in the S channel, without touching the balance of the body of the main instruments, present in the M channel. 
2. By means of the compressor It will be possible to slightly compress the S channel alone with a few dB of reduction (for example 2 or 3 dB), in order to contain the ambient effects during the most intense parts of the musical performance, allowing them to manifest themselves more in the more relaxed and rarefied points. This will allow you to increase definition and presence without losing spatiality. This effect can be more marked using a sidechain compressor that compresses the S channel according to the stresses of the signal present in the M channel. These compression techniques can also be used to obtain a compensatory effect in the case where, having chosen to raise the volume of the S channel to increase the spatiality of the mix, you still want to maintain the original sensation of presence intact.
3. With theequalizer You could lighten the bass in the side image by compensating for it appropriately by boosting the center channel, resulting in a firmer sound in the low frequencies; this trick can help improve the readability of the low end and the entire mix. Alternatively, depending on the case, it may be interesting to attenuate the "muddy" band between 200 and 400 Hz.

Optimizing the performance of your turntable stylus

In the case of mastering for vinyl record production, the total elimination of the lateral image in the low frequencies, achievable using theequalizer According to the technique described in point 3 above, it can become crucial for a more stable alignment of the turntable stylus, obtaining a more precise and clear sound, also avoiding any risk of the stylus “jumping” out of the groove, without increasing the weight adjustment of the turntable “arm”.

Improve tonal control between mix elements 

The ability to separately equalize the M and S channels will allow us, in part, to improve and balance the sound of the most important elements of the mix with respect to the other elements and the environment.

To give one example among many: we can act on the M channel to increase the presence of the vocal and snare drum in the mid-high range and at the same time to increase the bass in the kick drum and bass, without appreciably affecting the other elements of the mix and the ambience.

If the intervention described in the example produces an excessive harshness in the mid-highs and confusion in the lows, we can partially compensate for the intervention by attenuating the same frequencies in the S channel.

In this sense, with great caution and moderation we could attempt various compensatory experiments in order to improve readability and tonal balance, as an alternative to the normal tonal and dynamic correction performed in the LR environment during mastering.

Increase the loudness of the mix without affecting the rooms

Anyone who has tried to compress a master knows well that high ratio values can induce a “pumping” effect, which is particularly noticeable on the reverb, an inconvenience that must be contained through very careful use of the release parameters.

Instead, compressing only the M channel (in which the reverbs have less presence)  This drawback will be almost completely eliminated, allowing us to use stronger compression for the most critical elements of a pop-rock-dance mix, that is, the lead (for example the voice), the bass, the kick and the snare.

Obviously it will be appropriate to compensate for the volume reduction induced by the compressor by means of the make-up control (compressor output volume), in order to restore the pre-compression volume balances.

This compression operation requires a lot of moderation and attention to avoid compromising and distorting the original balance of the mix too much.

If the effect is unnatural, you can try reducing the ratio or slightly compressing the S channel as well (to a lesser extent).

Conclusion

• There matrix M/S for mastering It can be inserted at any point in the normal plugin chain: that is, before, in the middle or at the end of it, according to the needs that arise during the mastering process itself.
• It will also be possible to open multiple M/S matrices along the chain, for example: 

1. one at the beginning, dedicated to correcting the volumes of the central channel; 
2. after the tonal correction, a second one dedicated to refining the tonal correction; 
3. and maybe even a third after the dynamic correction, dedicated to refining the dynamic correction and fine-tuning the stereo image.

• However, unless it is particularly necessary, it may be advisable to limit the use of this technique in order not to overload the digital chain, also to prevent any possible cause of sound degradation.
• Finally, during and at the end of the operations it will be appropriate to compare it with the original mix.

N.B.

Some of the above processes (but not all) can be greatly simplified using some simple plugins (such as "Waves Center" and "Waves S1 Stereo Imager"). Once installed in a chain on the mix track, they will allow us to perform these functions with extreme convenience, offering immediate and intuitive results, albeit with some functional limitations.

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