Advertisement
MISTRUCTURE
OF THE SN-550
There are various types of noise; noise generated by a unit itself,
hum noise caused by the power supply line, noise caused by a
variable lighting system, a CRT display or computer.
Earlier noise reduction or noise gate units have been effective for
high pitch noise but not so for middle or low pitch noise.
Such devices
are almost useless for hum
caused
by power
supplics.
The SN-550,
however,
resolves such problems
with the latest
signal processing technology
while minimizing
tonal alteration
during the noise elimination process.
@ Noise
Canceling
How noise is actually perceived by a listener varies depending on
the volume difference between the audio signal and noise and/or
the difference in the frequency content of the audio signal and
noise. For example, when a sound is loud, you may not notice the
noise, but when the sound is low, the noise may audible.
Also,
even when the noise is low, if the frequency content of the audio
signal differs from that of the noise, the noise may be prominent.
The SN-550's noise canceling unit functions in response to the
situations described above.
The SN-550's noise canceling unit divides the audio signal into
five bands.
Each band has a noise suppresser.
When the input
signal drops below
the threshold
level, the noise canceling
circuitry will start working. That is, it controls the noise reduction
level depending on the level of the input signal.
When the
threshold level is raised, the noise reduction effect will be more
pronounced but the sound quality will be adversely affected.
To
achieve a satisfactory result you must set the threshold level while
actually listening to the noise reduction effect and the subsequent
sound quality alteration.
The SN-550's noise canceler reduces noise in individual frequency
bands as described above.
Noise Canceling
Characteristic
350, 700, 1.4 k, 28
k, 5.6 kHz )
(5 bands
:
Level
50 100
tk
10k
Frequency
(Hz)
@Hum
Canceling
The SN-550's hum canceling unit is an updated version of a unit
used in previous Roland products. This updated unit is even more
effective for removing hum and has less impact on the resulting
with sound quality.
Hum is a low frequency noise consisting of several harmonically
related frequencies and results from
the interaction of some
electronic device and the power supply.
Hum consists of the
harmonics related to the frequency of the power supply ( usually
50 or 60 Hz ). Ordinary hum cancelers remove these harmonics
by use of a "comb filter'. Hum noise can be reduced by using a
comb fijter, but it may alter or climinate portions of the audio
signal in the same frequency range.
To minimize such problems, the SN-550 uses a suppressor that
works only on the frequency that has the same harmonics as the
hum. The lower the input signal is below the threshold level, the
greater the hum canceling effect.
Frequency spectrum of the hum
(basic frequency:
60
Hz)
which is created
by the power
supply of a variable
lighting system
and picked up by a guitar's pick up.
Frequency
Hum
Canceling
Characteristic
(in 60 Hz steps)
|
Frequency
v
The hum
is removed.
Advertisement
