{
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  "slug": "sample-rate-conversion",
  "title": "Sample-rate conversion",
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  "lead": "Sample-rate conversion, sampling-frequency conversion or resampling is the process of changing the sampling rate of a discrete signal to obtain a new discrete representation of the underlying continuous signal. Application areas include image scaling and audio/visual systems, where different sampling rates may be used for engineering, economic, or historical reasons. For example, Compact Disc Digital Audio and Digital Audio Tape systems use different sampling rates, and American television, European television, and movies all use different frame rates. Sample-rate conversion prevents changes in speed and pitch that would otherwise occur when transferring recorded material between such systems. More specific types of resampling include: upsampling or upscaling; downsampling, downscaling, or decimation; and interpolation. The term multi-rate digital signal processing is sometimes used to refer to systems that incorporate sample-rate conversion.",
  "body": "Sample-rate conversion, sampling-frequency conversion or resampling is the process of changing the sampling rate of a discrete signal to obtain a new discrete representation of the underlying continuous signal. Application areas include image scaling and audio/visual systems, where different sampling rates may be used for engineering, economic, or historical reasons. For example, Compact Disc Digital Audio and Digital Audio Tape systems use different sampling rates, and American television, European television, and movies all use different frame rates. Sample-rate conversion prevents changes in speed and pitch that would otherwise occur when transferring recorded material between such systems. More specific types of resampling include: upsampling or upscaling; downsampling, downscaling, or decimation; and interpolation. The term multi-rate digital signal processing is sometimes used to refer to systems that incorporate sample-rate conversion. Movies (shot at 24 frames per second) are converted to television (roughly 50 or 60 fields per second). To convert a 24-frame/second movie to 60-field/second television, for example, alternate movie frames are shown 2 and 3 times, respectively. For 50 Hz systems such as PAL, each frame is shown twice. Since 50 is not exactly , the movie will run 50 / 48 = 4% faster, and the audio pitch will be 4% higher, an effect known as PAL speed-up. This is often accepted for simplicity, but more complex methods are possible that preserve the running time and pitch. Every twelfth frame can be repeated 3 times rather than twice, or digital interpolation (see above) can be used in a video scaler. Audio on Compact Disc has a sampling rate of 44.1 kHz; to transfer it to a digital medium that uses 48 kHz, method 1 above can be used with L = 160, M = 147 (since 48000 / 44100 = 160 / 147). For the reverse conversion, the values of L and M are swapped. Per above, in both cases, the low-pass filter should be set to 22.05 kHz. Multi-Rate Processing and Sample Rate Conversion: A Tutorial The Quest For The Perfect Resampler (PDF) Digital resampling by using polynomial interpolation. Farrow filter Using Farrow filter on the basis of piecewise cubic polynomial interpolation for digital signal resampling",
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    "title": "Sample-rate conversion",
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