M2TECH Evo Dac - Manual (Page 9)

E vo DAC
HIGH PERFORMANCE 192/32 DAC
REVISION P r A – SEPTEMBER 2011
Copyright © 2011, M2Tech Srl
9
M2Tech
www.m2tech.biz
5. Digital Audio connections and jitter
Usual digital audio connections all suffer, to a certain extent, a problem called jitter. Jitter is
an uncertainty in the timing of samples arrival to the DAC, due to the fact that the
connections carry more than one signal on a single wire or fiber: data, sampling frequency
and bit clock, all mixed in a way that the receiver can separate them.
Noise and the separation process itself produce jitter, which is then transferred to the
conversion IC. The final result is an analog signal affected by the jitter effects: a higher
noise floor and spurious (distortion tones) in the signal. Dynamic, low-level detail and
imaging all are affected by jitter
The only way to avoid injecting jitter into the conversion IC and, in turn, into the analog
signal without complicated retiming circuits is to transfer all three signals (data, sampling
frequency and bit clock) each on its dedicated wire. This is accomplished using I
2
S, an
audio signal transfer standard usually implemented inside equipment, between IC’s. An I
2
S
path is made of three wires (plus the ground reference).
Of course, I
2
S itself cannot ensure low jitter, as noise coupled to the sampling frequency
wire can still produce jitter. For this reason, the transmitter needs to use high current
drivers in order to reduce the line sensitivity to external noises coupled to its output
impedance. Moreover, the cable needs to be adequately shielded. M2Tech uses CAT-5
connectors and cables in order to provide good shielding of the delicate I
2
S signals. The
I2S output of the hi
F ace E vo is driven by high current drivers.
By connecting the hi
F ace E vo to the E vo DAC
using the I
2
S connection a virtually zero-
jitter transfer is implemented. This way, the great jitter performance of the hi
F ace E vo
USB interface can be transferred down to the
E vo DAC
analog outputs, allowing for a
sonic performance hardly matched by a plain S/PDIF DAC.
Even better performance can be obtained by powering
E vo DAC
(and hi
F ace E vo if used)
from the
E vo S UPPLY, which provides a cleaner supply than the stock wall adaptor. Less
supply noise means less jitter.