Thread: Soundcard FAQ
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Old 9th December, 2002, 04:15 PM
Aedan Aedan is offline
Chief Systems Administrator
Join Date: September 2001
Location: Europe
Posts: 13,075

Audio Quality questions

What are THD+N and THD?
THD stands for "Total Harmonic Distortion". It's a method for measuring how much distortion happens to an audio signal when it travels through a piece of equipment. The lower the percentage, the less distortion is occuring, and the cleaner the sound is.

THD+N is "Total Harmonic Distortion plus Noise". It's the same THD as above, but includes any noise generated by the equipment.

What is frequency response?
Frequency Response is a measure of how well a device can reproduce different frequencies of sound at the same level of loudness. Typically it states the lowest and highest frequencies (like 20Hz to 20kHz) and the "flatness" of the response (-3dB). Any soundcard that can really manage 20Hz to 20kHz with a flatness of -3dB is very high quality and probably supasses your ears! When looking at the flatness, ensure that the manufacturer is measuring to -3dB. If a larger figure is used, then the manufacturer is trying to make the frequency response look bigger than it really is.

What is Dynamic Range?
Dynamic range is a measure of the difference between the quietest (the noise floor) and loudest noise that can be played. The bigger the difference, the more capable the devices is of dealing with subtle sounds. A CD provides a Dynamic Range of about 90dB, a prerecorded cassette tape can manage about 50dB.

What is the noise floor?
The noise floor is the level of noise (or hiss) that the soundcard generate when it is not playing any sound. This represents the quietest sound that the soundcard can manage. The measurement is usually expressed as a negative number of decibels. The more negative the number, the less noise the soundcard introduces. (Look for a number better than -70dB)

How can I tell how good a soundcard is
The acid test for a soundcard is your ears. However, the specs can often provide an idea of how well the soundcard can manage sonic purity. The lower the THD and Noise figures, the better the card can perform in terms of keeping the signal pure. The flatter the frequency reponse, and the more true the sound will be. The bigger the dynamic range is, the more detail the soundcard can play.
Any views, thoughts and opinions are entirely my own. They don't necessarily represent those of my employer (BlackBerry).