Understanding THD+N
Total Harmonic Distortion plus Noise, or THD+N, is one of the most
common and widely used measurements made on audio devices.
Virtually every type of device used to produce, transmit, or process
audio signals has a THD+N specification.
Fundamentally, THD+N is a measurement of sound that is not
supposed to be there. If your device is creating a sound, you want it to
create that sound and nothing else. However, all devices create other
sounds as well.
The unwanted sounds break down into four basic categories:
.
Harmonic Distortion - unwanted sound that is related to the
desired sound.
.
Random Noise - unwanted sound caused by random
fluctuations in electronic components.
.
Interference - unwanted sound related to other signals within
the device or environment.
.
Hum - unwanted sound related to the frequency of the main
supply voltage.
Harmonic distortion is caused by slight imperfections in the creation or
recreation of the sound. These imperfections generally cause unwanted
sounds to be generated at whole-number frequency multiples of the
desired sound.
Random noise is created by almost every type of electronic
component. Noise sounds generally sound like ffff... and are generated
regardless of whether there is a desired sound being created or not.
Some noise exists at every frequency.
Hum is created by the main supply voltage leaking into the audio
signal. It exists at the frequency of the supply voltage and
whole-number multiples of this frequency.
Interference is caused by other signals leaking into the sound signal.
Crosstalk is a certain type of interference caused by sound leaking in
from other audio channels within the device.
The THD+N measurement includes all four types of unwanted sound.
If any of these are excessive, it will be noticeable in a THD+N reading.
FUNCTION Descriptions Understanding THD + N
4 Functions
ATS-1 Access User's Manual 4-11
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