and Linux support this standard. However, some USB sound cards do not conform to the standard and require proprietary drivers from the manufacturer. Cards meeting the older USB 1.1 specification are capable of high-quality sound with a limited number of channels, but USB 2.0 or later is more capable. 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 analyze 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 analyzed. There are programs that 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 80 dB below the fundamental; cards are available with distortion better than −100 dB. Sound cards with a sampling rate of 192 kHz can be used to synchronize the clock of the computer with a time signal transmitter working on frequencies below 96 kHz like DCF 77 with a special software and a coil at the entrance of the sound card, working as antenna. Driver architecture To use a sound card, the operating system (OS) typically requires a