Sample frequency conversion - Revision history

Brad Johnson at 00:11, 1 March 2012

2012-03-01T00:11:55Z

Brad Johnson at 00:09, 1 March 2012

2012-03-01T00:09:16Z

Brad Johnson at 00:07, 1 March 2012

2012-03-01T00:07:46Z

Brad Johnson at 00:05, 1 March 2012

2012-03-01T00:05:26Z

Brad Johnson at 00:05, 1 March 2012

2012-03-01T00:05:11Z

Brad Johnson at 20:43, 26 February 2012

2012-02-26T20:43:12Z

Brad Johnson at 20:35, 26 February 2012

2012-02-26T20:35:32Z

Brad Johnson at 20:34, 26 February 2012

2012-02-26T20:34:10Z

Brad Johnson at 20:32, 26 February 2012

2012-02-26T20:32:31Z

Brad Johnson at 20:28, 26 February 2012

2012-02-26T20:28:54Z

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 ==Overview==
-The term <nowiki>"Sample frequency conversion"</nowiki> and its abbreviation "SFC" are used interchangeably with the term "Sample rate conversion" its abbreviation "SRC." These terms are used to describe a process which employs DSP to re-sample digital audio at its original sample frequency and output it at a different sample frequency. The process can be either real-time or performed as a process on digital audio files.
+The term <nowiki>"Sample frequency conversion"</nowiki> and its abbreviation "SFC" are used interchangeably with the term "Sample rate conversion" its abbreviation "SRC." These terms are used to describe a process which employs DSP to re-sample digital audio at its original sample frequency and output it at a different sample frequency. SFC can either be a real-time process or an "off-line" process performed on digital audio files.
 ==History==

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 ==Overview==
-The term <nowiki>"Sample frequency conversion"</nowiki> and its abbreviation "SFC" are used interchangeably with the term "Sample rate conversion" its abbreviation "SRC." These terms are used to describe a process which employs DSP to re-sample a digital audio input signal at its original sample frequency and output a signal at a different sample frequency. The process can be either real-time or performed as a process on digital audio files.
+The term <nowiki>"Sample frequency conversion"</nowiki> and its abbreviation "SFC" are used interchangeably with the term "Sample rate conversion" its abbreviation "SRC." These terms are used to describe a process which employs DSP to re-sample digital audio at its original sample frequency and output it at a different sample frequency. The process can be either real-time or performed as a process on digital audio files.
 ==History==

@@ Line 1: / Line 1: @@
 ==Overview==
-The term <nowiki>"Sample frequency conversion"</nowiki> and its abbreviation "SFC" are used interchangeably with the term "Sample rate conversion" its abbreviation "SRC." These terms are used to describe a process which employs DSP to re-sample a digital audio signal input at its original sample frequency and output it at a different sample frequency.
+The term <nowiki>"Sample frequency conversion"</nowiki> and its abbreviation "SFC" are used interchangeably with the term "Sample rate conversion" its abbreviation "SRC." These terms are used to describe a process which employs DSP to re-sample a digital audio input signal at its original sample frequency and output a signal at a different sample frequency. The process can be either real-time or performed as a process on digital audio files.
 ==History==

@@ Line 1: / Line 1: @@
 ==Overview==
-The term <nowiki>"Sample frequency conversion"</nowiki> its abbreviation "SFC" are used interchangeably with the term "Sample rate conversion" its abbreviation "SRC." These terms are used to describe a process which employs DSP to re-sample a digital audio signal input at its original sample frequency and output it at a different sample frequency.
+The term <nowiki>"Sample frequency conversion"</nowiki> and its abbreviation "SFC" are used interchangeably with the term "Sample rate conversion" its abbreviation "SRC." These terms are used to describe a process which employs DSP to re-sample a digital audio signal input at its original sample frequency and output it at a different sample frequency.
 ==History==

@@ Line 1: / Line 1: @@
 ==Overview==
-The term <nowiki>"Sample frequency conversion"</nowiki> is interchangeably with the term [[Sample rate conversion]] and their abbreviations [[SFC]] and [[SRC]]. These terms are used to describe a process which employs DSP to re-sample a digital audio signal input at its original sample frequency and output it at a different sample frequency.
+The term <nowiki>"Sample frequency conversion"</nowiki> its abbreviation "SFC" are used interchangeably with the term "Sample rate conversion" its abbreviation "SRC." These terms are used to describe a process which employs DSP to re-sample a digital audio signal input at its original sample frequency and output it at a different sample frequency.
 ==History==

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 This example is of a very short average, between one and a few sample periods in duration, with an immediate return to accurate reproduction. The consequences of applying linear interpolation to an entire audio file would be quite unacceptable in high fidelity applications.
-High quality SFC requires much more sophisticated interpolation; and this requires large amounts of DSP to accomplish. The input data is typically "re-sampled" using interpolation to a sample frequency that is a multiple of the output sample frequency; so that samples "do exist" at the desired output SF. This technique is sometimes referred to as "[[over-sampling]]" and some form of over-sampling is also employed in contemporary audio converter design.
+High quality SFC requires much more sophisticated interpolation; and this requires large amounts of DSP to accomplish. The input data is typically "re-sampled" using interpolation to a sample frequency that is a multiple of the output sample frequency; so that samples "do exist" at the desired output SF. This technique is sometimes referred to as "[[over-sampling]]" and some form of over-sampling is also employed in contemporary audio converter design. High-accuracy interpolation involves including information from audio samples that occur both well before and after each audio sample in the computation; which increases both the time and processing power required to produce the results.
 [[Category:Terminology]]
 [[Category: Audio conversion]]

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 Because there is no information available in the original recording "between the samples;" the only way to generate "new samples" is to use some form of [[interpolation]]. The crudest method of interpolation is "linear interpolation" and as the name implies; is only accurate for a straight line. Because music waveforms are much more complex in nature than a straight line; more sophisticated methods of <nowiki>interpolation</nowiki> are required to produce acceptable results.
-One example of linear interpolation applied to audio is the audio CD standard. In order to achieve the goal of recording 75 minutes of stereo audio on a CD with the technology at the time; SONY/Phillips decided to employ a lower level of error correction than typical of computer data standards. This meant that errors beyond a certain size could not be completely corrected. Instead, linear interpolation (or "averaging") was employed as an "acceptable" means of partially correcting the error to avoid the possibility of more catastrophic results; such as a full-scale "pop," if the error was not corrected in some manner. Experience has shown that the audibility of averaging is very program dependent, and in many cases was fairly audible; especially when listening with headphones.
+One example of linear interpolation applied to audio is the audio CD standard. In order to achieve the goal of recording 75 minutes of stereo audio on a CD with the technology at the time; SONY/Phillips decided to employ a lower level of error correction than typical of computer data standards. This meant that errors beyond a certain size could not be completely corrected. Instead, linear interpolation (or "averaging") was employed as an "acceptable" means of partially correcting the error to avoid the possibility of more catastrophic results; such as a loud "pop," if the error was not corrected in some manner. Experience has shown that the audibility of averaging is very program dependent, and in many cases was fairly audible; especially when listening with headphones.
 This example is of a very short average, between one and a few sample periods in duration, with an immediate return to accurate reproduction. The consequences of applying linear interpolation to an entire audio file would be quite unacceptable in high fidelity applications.

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 ==Overview==
-Linear PCM recording employs equal "step-size" in both the [[time domain]] and [[amplitude domain]]. Accurate playback requires the "step-size" to be exactly the same in playback as in was in recording, with any variation from the ideal resulting in distortion. If the SF of a recording is changed during playback; the pitch and duration of the recording will change as a result. In order to change the sample rate without affecting the pitch or duration, new "samples" that are between the original samples on the timeline must be generated.
+Linear PCM recording employs equal "step-size" in both the [[time domain]] and [[amplitude domain]]. Accurate playback requires the "step-size" to be exactly the same in playback as it was in recording, with any variation from the ideal resulting in distortion. If the SF of a recording is changed during playback; the pitch and duration of the recording will change as a result. In order to change the sample rate without affecting the pitch or duration, new "samples" that are between the original samples on the timeline must be generated.
 Because there is no information available in the original recording "between the samples;" the only way to generate "new samples" is to use some form of [[interpolation]]. The crudest method of interpolation is "linear interpolation" and as the name implies; is only accurate for a straight line. Because music waveforms are much more complex in nature than a straight line; more sophisticated methods of <nowiki>interpolation</nowiki> are required to produce acceptable results.