Stereo Mastering and Mixing
When using the M/S matrix for mastering and mixing, the spatial image of the stereo signal can be controlled effectively. The BASE control alters the width of the stereo image from 0 %, mono, up to 300 % enhanced base width. The 100 % position has a center detent and is precisely calibrated. Stereo base enhancement in the range from 100 % to 150 % can improve the character of a stereo mix in a unique way. Depending on the structure of the mix, not only the stereo base is extended over the speakers but also three dimensional effects are possible. The mix seems to fill the space behind the stereo base line. Using such settings will also result in a different level balance between the channels; the direction control can be used to readjust identical levels in both stereo channels. The reason for the different levels is easy to understand. If a particular signal is located at the position 50 % to the right, it moves more to the right when the base control is set to more than 100 %. Apart from different phase relations between the channels also the level relation between the channels must change to achieve the enhancement. Depending on the structure of the mix and the setting of the base control the resulting balance offset occurs.

Stereo Mastering Set with M/S Matrix

With all base settings above 100 %, signal components of the right channel are increased on the right channel and reduced on the left channel as far as level is concerned. In addition, phase reversed signal components of the right channel appear in the left channel. The mono compatibly is the most critical issue using enhanced base width. When adding both stereo channels to mono all out of phase signals in both channels will be attenuated the more, the better the levels in both channels match. It is essential to check the mono signal after every change of the settings extensively when using this very interesting effect.

The elliptical Equalizer allows in some extend compensating the out of phase side effects. This device can be considered as some sort of frequency depending mono matrix that reduces the base width towards low frequencies with a steepness of 6 dB/oct. The human ear cannot locate any frequency below 300 Hz. The distance of the ears in combination with the reaction time of the brain determines this limit, since the wavelength of a 300 Hz signal is so long that the difference in level and time between the ears is not perceptible. In addition to this effect, a level difference of more than 15 dB in both stereo channels results in the effect that the signal is located from the one side only. This means that human ear cannot hear any difference between only one channel active and a level difference of 15 dB in the stereo channels. Of course, there are little, individual differences; someone may hear a difference of 1 or 2 dB more or less but this does not matter that much. Setting a crosstalk of 15 dB at 300 Hz that increases towards low frequencies will not result in audible differences as far as the location is concerned. However, such a setting reduces the base width of low frequency signals considerably and maintains a solid, centered bass fundament that reduces the mono compatibility problem when using stereo base enhancement. The elliptical equalizer of the TM130 M/S Matrix has a center detent at the 300 Hz / 15 dB crosstalk position, the control range is from less than 40 Hz up to 1000 Hz. Settings above 300 Hz may be audible; however, such settings can result in a good compromise between enhanced stereo and mono compatibility.

Stereo Microphones in M/S Mode
Together with two mic pre's, the TM130 M/S Matrix can be used for recordings with stereo microphones in M/S mode. The input mode select switch INPUT M/S changes the behavior of the input stage to accept M/S format signals instead of Left/Right signals. The outputs of the two mic-pre's are connected to the inputs of the matrix. The controls of the matrix make possible to modify base width and direction of the stereo signal as usual; the elliptical equalizer can also be used. The output stage converts the signal into the left/right format. A stereo microphone in M/S mode uses one of the two capsules with cardioid or omnidirectional characteristic while the second capsule is used with bidirectional characteristics. The cardioid capsule represents the M (mono) channel while the bidirectional (figure eight) capsule represents the S (side) channel. Both capsules are arranged at an angle of 90 °. The phase relation between the M microphone and the S microphone depends on the direction of the sound source. When the source is in the center position, the figure eight microphone has almost no output signal. A sound source from the left side results in an output signal on the S microphone with positive phase related to the M microphone, while a sound source from the left side results in an out of phase signal. In both cases the cardioid microphone has almost no output level. The directional pattern of a cardioid microphone depends on the frequency. With low frequencies the cardioid is rather wide, but higher frequencies result in a narrow characteristics. Using a stereo microphone in the conventional left/right mode requires to twist both capsules. A typical angle between the capsules is 90 °. In this case a sound source in the center position is not in the best possible position for the cardioid capsules, since both microphones are accentuated at an angle of approximately 45 °. This results in a lack of high frequency performance for the sound sources in the center position. Using M/S mode avoids this disadvantage .

The direction control of the matrix operates not in the way of a conventional pan pot or stereo balance control that cuts off one channel with settings all to the left or all to the right. Since the direction control operates in the M/S chain of the device, a setting all to the left results in a mono signal on the left channel only. Both input signals are always present; however, the relation between the output channels is changed. On the way from the center position to the left, the base width is reduced more and more and the right channel is attenuated while the right channel input signal is mixed to the left channel output.

The TM130 M/S Matrix is a 2U ToolMod module that fits into all available ToolMod Frames. As usual, horizontal and vertical versions are available.