DK-Audio MSD100

Oct 1, 2003 12:00 PM, By Mike Callaghan

The idea of using a Lissajous pattern to display stereo separation has been around as long as stereo recording — even to the point where dedicated oscilloscopes were built into audio equipment manufactured by Marantz. Heathkit even offered a stand-alone X-Y display for use with consumer stereo systems. These devices all used CRTs, and they all suffered from dim displays and the potential for burning of the phosphor if the audio went dead.

Early solid-state audio spectrum instruments used LED matrixes as displays, and resolution was limited by the number of LEDs that could be squeezed into the available area.

The MSD100 series from DK-Audio offers a bright, easily read display of both stereo separation and frequency dispersion. Taking full advantage of LCD technology, the display offers black-on-white as well as white-on-black images. The display brightness is controlled through a setup option and the front-panel buttons.

Three basic models of the display are available. The MSD 100 features analog inputs with unbalanced RCA connectors. The MSD100T/SA offers analog inputs with balanced XLR connectors. The MSD100AES/SA provides digital audio AES-3 inputs with balanced XLR connectors.

The different models provide a variety of basic functions:

• Phasemeter
• Audio vector oscilloscope
• Level meter with six selectable PPM/VU scales
• Individually selectable input reference levels with an additional 20dB of input gain
• LED overload indicators

The various functions are easily controlled using three buttons on the lower right corner. These select the display function, and allow muting of the left, right or both inputs. They will also increase the input sensitivity by 20dB, and are used to adjust the display brightness, the LCD viewing angle, reference levels, the PPM scales and to invert the black and white in the display.

In the stereo display mode, vertical bar graphs on the right side of the screen show left and right input levels. The ballistics of these bars can be rotated through VU, DIN, two different DMU and three PPM scales. A peak-hold function and individual reference level selections are also available. A pair of discrete red LEDs above the display show when excessive peaks are reached. A vertical bar graph at the left of the stereo displays the average phase relationship between the two audio signals, and indicates mono, stereo or reverse phase on a center zero scale.

The two, more enhanced models of the MSD100 include a pair of frequency spectrum displays; the traditional 1/3-octave bars show the energy distribution of the signal, and a FFT analyzer for more accurate definition.

Detail of the unit’s screen showing the Lissajous figure and level indication.

The 1/3-octave display uses a bank of filters for real-time frequency analysis. This provides a 31-bar display extending from 20Hz to 16kHz. Each bar shows a graphical and numeric visualization of the signal energy present in the specific band.

The FFT function uses a 1,024-band FFT algorithm to display signal content between 44Hz and 20kHz, covering the dynamic range between -70dBu to +10dBu. Rather than wide bars, the display consists of many thin vertical lines offering far greater resolution.

A mounting yoke is supplied with the MSD100, meant to place it on top of a console. Thumbscrews are provided to thread through the yoke into the sides of the chassis.

I elected to use the threaded yoke holes on the sides to mount the display in a rack panel with small angle brackets. The input connections are on the real panel along with the power connection.

At KIIS the unit mounts in the equipment rack adjacent to the processing equipment. It's fed with the de-emphasized left and right output of the off-air modulation monitor. It shows the all-important stereo balance, the channel phase relationships and also reveals when a CD was recorded with excessive clipping. (The ends of the stereo waveform flatten out into corners.) We can pull these out of the library until they're fixed. When the mic is all that's being used, anything other than a straight line means phasing trouble somewhere in the system. We typically run the left and right channel bargraphs in the VU mode, as that's what we're most used to.

The unit measures 179mm (w) x 129mm (h) x 39mm (d). Power is provided by a 15V wall-wart supply. The unit will operate from 12V to 30V ac or dc, and consumes 6.5W. The finish is an attractive gray and black, and the chassis is rugged and of heavy sheet-metal construction.

Display life in continuous operation is expected to extend well beyond two years. The unit was easy to install and set up. The different modes allow easy checking of what we're transmitting. Channel dropouts are easily detected, station processing is easier to set up and most of the time it just verifies that everything is running properly. We have found the unit to be a valuable tool for ensuring audio quality throughout the stations.