page 9
tions. Turning it one revolution slowly will result in a change of 12dB (24 x 0.5dB). As the rotation speed increases, each step goes
from 0.5dB to 2.0dB and then to 4.0dB. This allows not only precise control but also convenience when large volume changes are
desired.
Any changes made are reflected in the 7-segment display. Level range is from 0.0 to 99.5. NOTE: The least significant digit’s deci-
mal point (.) is used to indicate 0.5dB increments
aboUt S-loCk
tM
s-Lock
tm
is our proprietary PLL (Phase Lock Loop) circuitry that has been specifically developed for the m903 and its big brothers
the m904 and multi-channel controller, the m906.
When using the TOSLINK, S/PDIF, or AES2 digital inputs, the digital audio stream contains an embedded clock that can contain
various forms of jitter. The s-Lock PLL will lock to this clock source and provide an extremely stable and ultra-low jitter clock to run
the DACs.
s-Lock
tm
is a crystal-based PLL used for regenerating the incoming digital clock. The crystals used have extremely low intrinsic
jitter and are capable of locking to sample rates of up to 192kHz. When the digital input selected for the DAC is active, the s-Lock
circuitry automatically captures the incoming recovered clock from the AES3, S/PDIF, or TOSLINK connectors. Once phase-lock
with the incoming signal has been achieved, the DAC’s, which have been running off the original clock, are switched to run off the
ultra-low jitter s-Lock system clock. If at any time s-Lock is lost or not achieved, the DAC’s are run off the original clock. The s-Lock
system can effectively lock to input sample rates of 44.1kHz or 48kHz +/- 5Hz, 88.2kHz or 96kHz +/- 10Hz and 176.4kHz or 192kHz
+/- 20Hz.
If the incoming digital audio signal clock frequency is outside of these tolerances the s-Lock circuit will not lock and the s-Lock
indicator on the m903 will extinguish. Even if the s-Lock does not achieve lock, the digital audio receiver circuits in the m903 can
achieve excellent recovered clock jitter performance. Note that in USB mode, the m903 is the clock master so there is no need to
“lock” to an incoming signal.
aboUt x-feeD (CroSSfeeD)
When listening to loudspeakers in a room, your left ear hears sound primarily from the left speaker (and vice versa) but also
receives a signal from the right speaker at a lower level and with some time delay compared to the right ear. As well, the right
speaker sound that reaches the left ear does not have a flat frequency response as the sound waves have traveled around the
shape of your head before reaching your left ear. The brain uses delay, level and frequency response characteristics to process the
location of a sound and hence, create an aural image.
When listening through headphones, each ear only hears the sound from one transducer and the mixing of signals between the
ears does not exist. In this situation the brain is left without many of the psycho acoustic clues required to generate a properly
distributed image and an accurate sound stage. The result is that instruments seem to cluster in the far left, far right or center of
your head. Since the vital clues are absent, the brain has a difficult time deciding how to process the sounds coming from the
headphone, which can result in listening fatigue when listening for extended periods of time.
The m903 contains circuitry which electronically simulates the signal crossfeed that occurs in a real acoustic space and helps the
brain establish instrument locations across the entire sound stage. While it is difficult to perfectly model the very complex level,
delay and frequency response characteristics of the head, the crossfeed circuitry in the m903 gives the brain some of the basic
clues it needs and the result is a very pleasing simulation of an acoustic space.
After extensive research and listening to many different crossfeed circuits, we chose to license and implement an existing cross-
feed circuit design called “The Natural Crossfeed Filter” which was designed by Jan Meier of Meier-Audio (
).
This is an updated version of the crossfeed in the m902, which has slightly more pronounced effect and also gently compensates
for the perceived loss of bass response with some program material.
Accessing And Using The Setup Menu
The m903 features a number of useful functions that can be accessed and adjusted using the setup menu feature.
To access the m903 setup menu, simply press and hold the front panel encoder knob for 3 seconds. Once the m903 has entered
the setup menu, you will see the 7-segment display change to reflect the currently activated setup menu mode.
To navigate through the available setup menu items, simply rotate the encoder knob, which will scroll you through the available
modes, either clockwise or counter-clockwise. Once the last mode is reached, continuing to rotate will loop you back to the first
mode.
