Stereo Mastering

M/S Matrix with Stereo Base Width Control, elliptic EQ and Equalizer in the M/S Chain.

Influencing the spatial image of the stereo signal using the special possibilies of the M/S principle is a very powerful way to achieve huge improvements of a stereo mix. With stereo mastering, this principle allows direct access to the stereo base width and the direction for boosting up and repair work of any mix with amazing results.

Equalization, integrated in the M and S chain, is a very important feature for M/S processing. In difference to usual stereo equalizers that treat the left and right channels in parallel, the M/S eq's treat the equivalent signals M and S separately. The effect on the frequency response is minor; a lot more important is the possible variation of the stereo base width in a particular frequency band that results in stunning improvements that are not possible with any other kind of treatment.

Using the equalilzers in the S channel results in an additional impression of depth behind the speakers, while treatment of the M channel can produce a stable, centered bass fundament of the mix.

The W785MS module can be used to add 5 equalizer bands to the internal EQ bands for extensive M/S treatment.

In addition to the M/S equalizers, all conventional controls of an extensive stereo direction mixer are existing. The stereo base width control allows variation from mono (0) via 'stereo unchanged' (1) to over base. The range above 1 widens the stereo base width up to 150 %, which in a usable range for mastering applications. The direction control affects the left-right relation of the stereo signal. The control range of +/- 4 dB is adapted to mastering and allows precise correction of the channel balance.

The elliptical equalizer reduces the base width at low frequencies and maintains mono compatibility of bass signals. The side effects of base enhancements on the mono compatibility can be reduced by centering the low frequency range with the elliptical EQ, without audioble reduction of the base width.

Inputs and outputs can both operate in left/right or M/S mode. The module can also be used to convert from one format to another.

The graphic shows the mastering version of the W731 with control ranges adapted to this application. Another version that is adapted for recording with stereo microphone is here.

Modification of the stereo base with the equalizer bands is an extremely effective feature for mastering. In difference to the effects caused by over base settings of the base width control that operates frequency independent, using the equalizers results in similar improvements that can be controlled more precisely and will cause less problems as far as the mono compatibility is concerned. Using the EQ's appropriately can result in a well centered, tight bass range and an impressive width and depth of the mid and high range. Nobody who had the opportunity to test this principle wanted to go without these possibilities in the future.

The M/S Equalizers
The equalizers treat the frequency response in the M and the S channel. The low EQ is located in the M channel, while the mid and high EQ's are located in the S channel. The low equalizer affects only the mono components of the stereo signal, while the settings of the mid and high EQ's affect only the spatial signal components. Boosting the low EQ results in a reduced base width in that range, while boosting with the mid and high bands enhances the base width. These EQ settings are pratically not audible in mono but result in effective changes in the spatial image, width and depth of the stereo signal.

In addition to the 3 integrated EQ bands, the 5-Band Equalizer W785MS can be installed in an insert point of the W731 matrix to increase the number of EQ bands in the M/S chains.

Using these equalizers effectively results in amazing improvements; however, any improvement can cause problems of the mono compatibility of the stereo mix. It is absolutely necessary to check the mix in mono after changing any setting.

The elliptical Equalizer
The elliptical Equalizer completes the feature set of the M/S direction controller W731. The elliptical EQ causes frequency dependent crosstalk, that increases towards lower frequencies, which reduces the phase reversed signal components and centeres the bass range. Since human ear cannot locate any signals below a frequency of 300 Hz, the effect of the elliptical EQ is not audible unless you set the frequency control to values above 300 Hz. Even such a setting can result in an improvement, since it offers higher mono compatibility that can make a higher base width setting possible. The section causes 15 dB crosstalk at the selected frequency. The steepness is 12 dB/oct.

Control Ranges of the Mastering Version
The control ranges of the mastering version of the M/S matrix are adapted to mastering applications. While the control range of the stereo base width ranges up to 300 % with the recording version, it is reduced to 150 %. The very important range between 100 % and 150 % allows precise regulation in small steps of 5 %. In addition, the control range of the direction control, which reaches from 'mono from left' to 'mono from right' with the recording version, is reduced to +/- 4 dB, since this control is used to compensate small differences that result from base width modifications with mastering. The reduced control ranges allow precise regulation in small steps.

The range of elliptic equalizer if not different in both versions and reaches up to 1 kHz for 15 dB crosstalk. The M/S equalizers are not different in both versions as far the sweep ranges and the q-factor control ranges are concerned; however, the boost/cut ranges are reduced to +/- 10 dB and the range around the center position is expanded to allow settings that are barely audible. The first steps next to the center causes boost or cut of 0.5 dB. The sweep ranges are 20 Hz to 2 kHz for the low eq in the M chain, 500 Hz to 25 kHz for the mid EQ, and 1 kHz to 30 kHz for the shelving high EQ, both located in the S chain. The q-factor control range is identical for the low and mid eq and covers the range from 2 octaves down to a third.

The Module
The M/S matrix is hard-bypassed unless the DIR-ON switch is pressed. There are additional bypass switches for the M/S equalizer and the elliptical EQ..

An internal insert point makes possible to integrate the M/S extension 5-band equalizer W785MS into the device. The insert point is available on the 25-pin D-Sub connector in the frame. A special cable that belongs to the scope of supply of the W785MS is necessary. The external eq bands are active when the EQ switch in the W731 is pressed and the W785MS is switched on. The bypass switch of the W785MS activates the insert point automatically.

Inputs and outputs of the module are balanced and available in electronically balanced and transformer balanced versions as well. The transformer version uses oversized torodial transformer, brand Haufe, Germany. The maximum level is more than + 30 dBu.

The W731 is a single slot V700 module that can be installed in all standard frames.

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Manual:  HTML  |  PDF 
fits into Standard Frames
ToolMod Stereo Mastering
W785 M/S Extension Equalizer
for W731 M/S Matrix
open V700 Navigation Page
Control Range Stereo Base Width from
0 to 120 % up to 0 to 300 %
Boost/Cut Control Ranges of the EQ's from
+/- 6 dB to +/- 16 dB
Custom Colors of
Faceplate and Control Knobs
W730 - M/S Matrix, Stereo Direction Controller and elliptical Equalizer
W732 - M/S Matrix
ToolMod MS-Processor
W785MS - M/S Extension Equalizer with 5 additional EQ bands for W731

M/S Basics
The M/S matrix converts a stereo signal from the conventional left/right format into the special M/S format. The W731 matrix allows to switch inputs and outputs either to left/right mode or M/S mode indepently.

The M/S format uses the M channel for the mono components of the stereo signal while the S channel contains all spatial components. Both formats can be converted to each other; a matrix is necessary for the conversion. The M/S format offers possibilities to control the spatial parameters 'Width' and 'Direction' directly, which is not possible in the left/right format. Any changings of level and/or phase in the S channel in relation the M channel results in changings of the stereo base width. When the S signal is muted, only the mono components remain present.


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