Uses
The main function of a sound card is to play audio, usually music, with varying formats (monophonic, stereophonic, various multiple speaker setups) and degrees of control. The source may be a CD or DVD, a file, streamed audio, or any external source connected to a sound card input.
Audio may be recorded. Sometimes sound card hardware and drivers do not support recording a source that is being played.
A card can also be used, in conjunction with software, to generate arbitrary waveforms, acting as an audio-frequency function generator. Free and commercial software is available for this purpose; there are also online services that generate audio files for any desired waveforms, playable through a sound card.
A card can be used, again in conjunction with free or commercial software, to analyse input waveforms. For example, a very-low-distortion sinewave oscillator can be used as input to equipment under test; the output is sent to a sound card's line input and run through Fourier transform software to find the amplitude of each harmonic of the added distortion. Alternatively, a less pure signal source may be used, with circuitry to subtract the input from the output, attenuated and phase-corrected; the result is distortion and noise only, which can be analysed.
There are programs which allow a sound card to be used as an audio-frequency oscilloscope.
For all measurement purposes a sound card must be chosen with good audio properties. It must itself contribute as little distortion and noise as possible, and attention must be paid to bandwidth and sampling. A typical integrated sound card, the Realtek ALC887, according to its data sheet has distortion of about 80dB below the fundamental; cards are available with distortion better than -100dB.
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