Glossary; Sampling Frequency - NAD 118 Manuel D'installation

GB

7. GLOSSARY

ABSOLUTE PHASE
See "Polarity"
ADC
Analogue to Digital converter. Refer also to chapter
"Introduction"
DAC
Digital to Analogue converter. Refer also to chapter
"Introduction"
DSP
Digital Signal Processing
GAIN
Amplification factor; for the Model 118 the input sen-
sitivity (and therefore the amplification factor) for the
analogue sources can be changed to prevent overload-
ing of the ADC (signal too loud) or not exploiting the
ADC to its full potential (signal too low).
Infrasonic filter Filter to remove the lowest frequen-
cies. Most loudspeakers cannot reproduce these fre-
quencies yet the presence of these frequencies can put
a significant strain on both power amplifiers and loud-
speakers, in which case it is best filtered out.
PEAK
Sudden burst in the signal which can cause distortion
if it overloads the ADC and/or DAC, indicated by the
Peak LED (23). Setting the input gains, high gain and
system sensitivity controls and switches correctly
avoids overload.
POLARITY
The sound shock wave created by hitting e.g. a drum
starts with an increase of the air pressure, (represented
normally as a positive electrical signal), then as the
sound progresses in time, air pressure will rapidly
decrease, represented as a negative signal. All this
happens very fast, the slowest audible change (very
low frequencies) from positive to negative and vice
versa is approximately 40 times per second.
An analogue audio signal will change continuously in
value from negative to positive and vice versa, a direct
representation of sound. A good loudspeaker will trans-
form this electrical signal exactly as changes in air
pressure (sound) by rapidly moving the cone(s) in and
out.
Please refer to graphs opposite; the signal in figure
B is identical to that of figure A, but with reversed polar-
ity (the length of time of the shown signal is extremely
short, a fraction of a second). The peaks and troughs
which are on the positive side at figure A are now at the
negative side in figure B.
NAD
18
A
+
–
normal
Analogue representation of an audio signal
B
+
–
same signal, polarity reversed
B. Normal same signal, polarity reversed

SAMPLING FREQUENCY

The frequency with which an ADC or DAC calculates
the digital signal. Three different sampling frequencies
are commonly used: 32kHz for radio and television
broadcasts, 44.1kHz for CD and 48kHz for DAT.
time
time