Phase; M/S Processing; Lo Cut - RME Audio Micstasy User Manual

9.4 Phase

PHASE changes the polarity (180°). Phase cancellations and sound changes can be caused by
using multiple microphones at different places, or wrongly soldered cables. In such cases
PHASE can eliminate the error by adding an additional phase inversion.
The signal path of the Micstasy is fully symmetrical, from the input up to the AD-converter. The-
refore the function Phase is realized passively by a simple relay, swapping the positive and
negative signal line. With this, Phase operates fully transparent and causes zero change of the
audio signal.

9.5 M/S Processing

The mid/side principle is a special positioning technique for microphones, which results in a mid
signal on one channel and a side signal on the other channel. These information can be trans-
formed back into a stereo signal quite easily. The process sends the monaural mid channel to
left and right, the side channel too, but phase inverted (180°) to the right channel. For a better
understanding: the mid channel represents the function L+R, while the side channel represents
L-R.
The Micstasy includes a digital M/S processor. Therefore the analog output signal stays un-
changed. Also the channels have a fixed assignment: all odd ones are M, all even ones are S.
The front panel shows an according labelling:
Channel 1 M/S (D)
Channel 2 M/S (D)
The M/S-Processing automatically operates as M/S encoder or decoder, depending on the
source signal format. When processing a usual stereo signal, all monaural information will be
shifted into the left channel, all stereo information into the right channel. Thus the stereo signal
is M/S encoded. This yields some interesting insights into the mono/stereo contents of modern
music productions. Additionally some very interesting methods of manipulating the stereo base
and generating stereo effects come up, as it is then very easy to process the side channel with
Low Cut, Expander, Compressor or Delay. The most basic application is to change the level of
the side channel: this allows to manipulate the stereo width from mono to stereo up to extended
in a step-less way.

9.6 Lo Cut

LO CUT activates a high-pass (bass removal) with 18 dB per octave, at a cut-off frequency of
65 Hz. This filter can remove rumble, subsonic-noise and other low frequency noises.
The LO CUT of the Micstasy shows a slow roll-off in the frequency response, without any reso-
nance rise. The circuit design provides low THD figures, which unfortunately is not taken for
granted. Even very expensive devices sometimes incorporate Lo Cut filters that cause relatively
high distortion of about 1%. The basic filter of the Micstasy is THD optimized. It generates even
at already low 20 Hz a distortion of only 0.13 %. Note that here the fundamental signal is al-
ready attenuated by 34 dB. The special symmetrical design with two filters further lowers the
distortion to 0.08 %. At the same time linearity and noise are improved. At 30 Hz and 22 dB
attenuation the distortion is down to 0.03 %. Thus the sum of all generated harmonics is 69 dB
below the fundamental, which is again already lowered by 22 dB – and is therefore without any
meaning.
User's Guide Micstasy © RME
17