SPL M/S Master – Mid/Side Mastering Processor


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SPL Electronics


SPL M/S Master Mid/Side Mastering Processor

The SPL M/S Master Mid/Side Mastering Processor, your key to access the mid and side information of a mix. Discover the classic alternative to the L/R format and adjust the M/S proportions yourself!

SPL M/S Master Mid/Side Mastering Processor Details

The M/S Master is your key to access the mid and side information of a mix. Discover the classic alternative to the L/R format and adjust the M/S proportions yourself. Insert all your outboard gear via intelligent send/returns and use it for L/R or M/S processing at the touch of a button.


Our ability to identify the direction and distance of a sound source is the essence of spatial hearing. The human ear can identify level and time differences from ear to ear very precisely and use that information to localize sound. At frequencies up to 1500 Hz the ear analyzes basically time differences to localize sound, while above this frequency it uses level differences.

Our hearing provides excellent conditions to apply room information even to artificially generated sounds. Regardless of the deficiencies and differences that loudspeakers and headphones might present during playback, the human ear needs only the signals to be codified in, at least, two channels, in order to be able to identify time and level variations, which result in spatial hearing.

This sort of recording and playback that includes spatial information is known as stereophony (from Greek stereos = solid or three-dimensional). The resulting stereo image is called panorama. Besides the two-channel stereophony there are several other formats of stereophony. The common conception of “stereo” as a two-channel recording is thus incorrect.

M/S Stereophony

Equally incorrect is the concept that the encoding of a stereo signal is always done in a right and a left channel. This idea is based on the fact that we have a right and a left ear and that all two-channel recording and playback systems use the same right/left format. It is also not true that all recordings are made with a microphone for the left channel and a microphone for the right channel.

The differences between the most important microphone techniques have much more to do with level and time differences. Due to the advantages and disadvantages that each technique provides, more often than not they are combined during production to achieve L/R playback.

While there are several stereo techniques that can be applied during miking, for signal processing during production there is only one technique that is actually useful: M/S. “M” stands for Middle (or Mid) and “S” for Side, which means that signals are separated from the middle to the sides, instead of from left to right. M/S can be actually applied during recording: two microphones with different polar patterns record direct and spatial information.

M/S Encoding

Besides the microphone technique, M/S can also be used as an alternative stereo encoding for signal processing, which means that signals do not necessarily need to be recorded with the M/S microphone technique to be able to apply M/S encoding afterwards (at the mastering stage, for example).

In fact, M/S encoding can be generated from L/R encoding by summing and subtracting signals:

M = L + R, S = L â?” R

The sum of the left and right signals in the Mid signal corresponds to the mono signal of the L/R encoding. The Side signal is also created from the L/R signal by inverting the polarity of the right channel. The sum of phase-inverted signals results in the cancellation of mono information in the signals summed; thus, the Side signal is made up of the differences between L and R. The detailed formula may be clearer: M = L + R, S = L + (-R). The minus sign stands for the phase inversion.

It is also possible to create a L/R signal encoding from an M/S encoding by summing and subtracting the signals, what is usually called M/S decoding:

L = M + S, R = M – S

Mathematically, the sum and subtraction of signals guarantees a lossless conversion from L/R to M/S and back to L/R, which is a very important aspect for using M/S encoding for signal processing.

M/S Happens

M/S encoding is also used for VHF radio transmission. In this case, the Mid signal is sent with much higher energy. If the reception is not very good, a stereo receiver can switch to mono to retain the most important information. A mono receiver will always receive a mono compatible signal.

Equally beneficial is M/S encoding when using “Joint Stereo” compression with MP3. As long as there is almost no information in the side signal, the compression rate can be higher as with L/R encoding.

Thus, in audio production M/S encoding is the best way to ensure full mono compatibility. M/S encoded signals provide an adequate way to control and ensure mono compatibility: the reduction of the Side signal results in the increase of the mono signal.

M/S Mastering

The use of a mid (M) and a side (S) signal instead of the usual L/R signal results in a much wiser musical processing.

High-energy Mid signals (vocals, snare, bass guitars, etc.) can be easily separated from Side signals (guitars, keyboards, cymbals, etc.). When mastering sum signals, M/S encoding is often the best option to be able to target single elements within a mix.

The M/S Master allows you to directly correct the balance in the mid frequency range and improve the depth and transparency of stringed instruments. Thanks to the inserts you can also use filters and effects (compressors, EQs, De-essers) more precisely. Thus, elements like vocals can be processed without affecting the overall ambience â?” removing vocal sibilance doesn’t affect cymbals, for example. On the other hand, the stereo image can also be enlarged without affecting the mono information. Not to mention the fantastic possibilities to process ambience that M/S encoding provides.

SPL M/S Master Mid/Side Mastering Processor Features

  • Analog tool for M/S encoding
  • Active control of M/S mix ratio
  • Seamless integration of external processors
  • One-button insertion of outboard gear in the M/S or L/R path
  • Different VU-meter modes
  • Low cut filter for the Side signal
  • FLOAT function for better mono compatibility

SPL M/S Master Mid/Side Mastering Processor Applications

  • Stereo image enhancement after mixdown or during mastering
  • Reverb and ambience reduction without losing brilliance
  • Independent processing of rhythmic elements, pads and other sounds placed off the center of the stereo image without affecting central elements, and viceversa
  • Precise EQ processing of elements that sound too dull
  • Specific dynamic correction of lively parts
  • Dynamic reduction in Side elements without affecting drum transients

SPL M/S Master Mid/Side Mastering Processor Specifications

Inputs & Outputs

  • Electronically balanced instrumentation amplifiers
  • Sockets: XLR
  • Input impedance: 20 kOhm balanced/10 kOhm unbalanced
  • Output impedance: 150 Ohm balanced/75 Ohm unbalanced
  • Max. input level: 20 dBu
  • Max. output level: 20 dBu


  • Frequency response (-3 dB): 10 Hz – 100 kHz
  • Common mode rejection ratio: â?º 60 dB (@ 1 kHz, 0 dBu input level and unity gain)
  • Total harmonic distortion & noise: 0,007 % (@ 1 kHz, 0 dBu input level and unity gain)
  • Signal to noise ratio (A-weighted): -82 dB
  • Dynamic range (unweighted): 102 dB

Power Supply

  • Toroidal transformer
  • Fuses: 230 V AC, 50 Hz: 315 mA; 120 V AC, 60 Hz: 630 mA
  • Voltage selector: 115V/230V
  • Power consumption @ 230 V: 9,1 W/10,8 VA ; @ 115  V: 5,6 W/7,1 VA

Dimensions and Weight

  • Housing (W x H x D): 482 x 88 x 320  mm (depth including controls and sockets)
  • Weight: 3.6 kg/7.94 lbs

SPL M/S Master Mid/Side Mastering Processor Downloads