Owners Manual

PAGE 7
Volume and Mute Control
A high quality, light action stepped rotary encoder is used for volume and mute func-
tions. Turn the knob clockwise to increase volume, counterclockwise to decrease the vol-
ume. A single push and release will mute all outputs. When the unit is muted, the 7 segment
LED will dim and pulsate to indicate mute is active. Another single push and release de-ac-
tivates mute. The m900 attenuator is a hybrid design. Most of the volume control duties are
handled in the digital domain with 32 bit processing but there are two analog gain ranges
as well. This allows a full 99dB of volume control range, preserves a very low noise floor for
IEMs, and allows high peak output voltage for low efficiency planar magnetic phones.
Crossfeed Circuitry
A completely analog crossfeed circuit electronically simulates the signal crossfeed that
occurs in a natural acoustic space. The crossfeed function can be switched on or off from
the Setup Menu.
How does crossfeed work? 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.
However, 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 dis-
tributed 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 m900 contains
crossfeed 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 m900 gives the brain
some of the basic clues it needs and the result is a very pleasing simulation of an acoustic
space while maintaining the tonality and balance of the original source.