grace design
m
902
owner’s manual
11
will take this clock source and provide an extremely stable and ultra-low jitter clock to run the DACs.
The goal, of course, is pristine audio. We think you’re going to love s-Lock so here’s a bit more detail on
how this works:
s-Lock 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 AES3, S/PDIF, TOSLINK, or USB. Once phase-lock with the incoming signal has
been achieved, the DACs, 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 DACs are run off
the original clock. The s-Lock system can effectively lock to input sample rates of 44.1kHz or 48kHz +/-
10Hz, 88.2kHz or 96kHz +/- 20Hz and 176.4kHz or /- 40Hz.
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 m902 will extinguish. Even if the s-Lock does not achieve lock,
the digital audio receiver circuits in the m902 can achieve excellent recovered clock jitter performance.
abouT x-feed
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
psychoacoustic 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 m902 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 cross feed circuitry in the m902 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 licence and
implement an existing crossfeed circuit design called “The Natural Crossfeed Filter” which was
designed by Jan Meier of Meier-Audio (www.meier-audio.de).
