Published on February 20, 2008
Technically, there are two main types of distortion that can become problems: THD (total harmonic distortion) and TID (transient intermodulation distortion). These happen within the circuitry and are not caused by outside factors.
Circuit designers need to minimise distortion as much as they can in order to produce good sound quality.
THD is produced as the main sound waves are delivered and is twice as high in terms of frequency. For example, if the main sound wave is 1000Hz, then the THD will be 2,000Hz.
This is very difficult to avoid and when designing an audio circuit, the designer needs to minimise this type of distortion as much as possible. THD is affected by circuit design as well as the quality of components. However, THD is usually lower as the frequency increases.
The other type of distortion that affects sound quality significantly - TID - happens whenever more than two frequencies are fed into an audio circuit.
The relativity of the two frequencies can be positive or negative. For example, when frequencies of 16 and 17KHz are fed and the difference is measured, the result is not the same as the THD, which is measured from one frequency.
TID takes place temporarily and the higher the frequency, the higher the TID. Distortion will be great when the recording is unable to capture all the frequencies, especially when there are powerful signals. For example, when switching the amplifier on or off, you can hear the "pluck" sound from the speakers.
Another problem is "crosstalk", which means the leaking of signal from one channel to the other, resulting in loss of clarity. This happens more at higher frequencies than lower frequencies and is usually caused by imperfect circuit design.
Multi-channel amplifiers can suffer more from this problem, while designers have found that the power supply also affects this leaking of the signal.
Noise can also sneak into different channels and cause a loss of signal flatness. Therefore, a good amplifier needs to have a high-quality power supply, which can even be used to measure the sound quality between amplifiers.
For can amplifiers, the distortion is usually external more than internal. The audio components are powered by direct current from the battery, and if the power is not enough, various distortions can creep into the circuit.
So it is important to choose high-quality equipment and to make sure there is enough power before all kinds of distortions start to show up in your system. Using systems that are not complex and have few connections can also lower the chances of distortion.
By Wijit Boonchoo
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