Many audiophiles have this experience: in daily music
playback, the more instruments played, the greater the background noise of the music, especially the classical music played
by a large orchestra, the background noise may reach intolerable levels.
Where does this background noise come from?
For high-end equipment, the biggest sources of background noise are mainly in the following two aspects.
distortion. People have known the influence of intermodulation distortion for a long time, so the current technology can make
the intermodulation distortion of the amplifier very small.
2) Phase distortion. Phase distortion can cause background
noise. At present, this issue has not attracted enough attention from everyone.
Because music information contains
countless frequency components. Therefore, for music electrical signals, phase distortion means that the phases of the various
frequency components in the music spectrum are not completely consistent.
Regarding the relationship between phase
distortion and background noise, for those who know some electronic technology, you can read "Music Electrical Signals
and Spectrum" to have a deeper understanding. Or, we only need some basic physics knowledge to understand the relationship
between background noise and phase distortion:
1. The sound that shouldn't be there is noise.
2. If there is
noise, there must be some energy that generates the noise.
3. The energy that should not appear at a certain point in
time is the energy that generates noise.
4. The phase distortion is the distortion in the time domain, that is, the
signal is misaligned on the time axis.
5. The result of phase distortion is that certain energy on the music signal
track is misaligned on the time axis.
Or we can take residential electricity in the United States as an example. Civilian electricity in the United States is a two-phase power source, and the phase
difference between the two power lines should be 180 degrees. Phase distortion means that the phase difference between the
two phases is not equal to 180 degrees. With phase distortion and without phase distortion, their two-phase combined waveforms
are different. The difference component between these two different waveforms is equivalent to what we now call background
In the audio system, every equipment including cables may produce phase distortion.
CD player. Jitter
of the system clock or checksum data errors can produce phase distortion. In the analog filter after D/A conversion, if its
cut-off frequency is close to the effective frequency, it will produce phase distortion.
Preamplifier. Band limitation
and tone control functions can produce phase distortion.
line amplifier. Generally, the phase distortion of the line
amplifier is smaller than that of the preamplifier.
Analog equalizer. According to different degrees of adjustment
depth, the analog equalizer will produce phase distortion from weak to strong.
Power amplifier. Various measures to
limit the signal frequency band and deeply suppress overshoot will produce phase distortion.
For all audio equipment,
the lower the conversion rate (V/us), the greater the chance of phase distortion.
Speaker. The uneven phase characteristics
of the loudspeaker reflect the degree of phase distortion.
Audio cable. In the audio system, the cable has a longer
transmission distance than other circuits, so the cable has the greatest chance of producing phase distortion. Because the
music signal has a wide frequency band of 10 octave. It is difficult for the various frequency components on the music signal
spectrum to achieve complete agreement in time during the transmission of the cable. After the music signal is transmitted
over a long distance, some frequency components are misaligned on the time axis (phase distortion).
For high-end equipment
systems, if you are not using an analog equalizer or tone function, cables may be the biggest source of background noise.
Created by Chen
Last revision date: Jul-2021