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.

1) Intermodulation 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 noise.

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