![]() ![]() ![]() The Digital Audio Tape (DAT) format was released in 1987 with 48 kHz sampling. Some digital audio was provided for domestic use in two incompatible EIAJ formats, corresponding to 525/59.94 (44,056 Hz sampling) and 625/50 (44.1 kHz sampling). ![]() in UK and Japan), because this is sufficient for FM stereo broadcasts, which have 15 kHz bandwidth. In the early 1980s, a 32 kHz sampling rate was used in broadcast (esp. A 50 kHz sample rate, used by Soundstream in the 1970s, following a 37 kHz prototype. Several other sampling rates were also used in early digital audio. The 88.2 kHz and 176.4 kHz rates are primarily used when the ultimate target is a CD. Various halvings and doublings of 44.1 kHz are used – the lower rates 11.025 kHz and 22.05 kHz are found in WAV files, and are suitable for low-bandwidth applications, while the higher rates of 88.2 kHz and 176.4 kHz are used in mastering and in DVD-Audio – the higher rates are useful both for the usual reason of providing additional resolution (hence less sensitive to distortions introduced by editing), and also making the low-pass filtering easier, since a much larger transition band (between human-audible at 20 kHz and the sampling rate) is possible. NTSC has 490 active lines per frame, out of 525 lines total PAL has 588 active lines per frame, out of 625 lines total.Ĥ4,100 is the product of the squares of the first four prime numbers ( 2 2 ⋅ 3 2 ⋅ 5 2 ⋅ 7 2 ) and hence has many useful integer factors. 44.1 kHz was deemed the highest usable rate compatible with both PAL and NTSC video and requiring encoding no more than 3 samples per video line per audio channel. To enable reuse with minimal modification of the video equipment, these ran at the same speed as video, and used much of the same circuitry. The 44.1 kHz sampling frequency allows for a 2.05 kHz transition band.įurther information: PCM adaptor § OperationĮarly digital audio was recorded to existing analog video cassette tapes, as VCRs were the only available transports with sufficient capacity to store meaningful lengths of digital audio. The wider this transition band is, the easier and more economical it is to make an anti-aliasing filter. While an ideal low-pass filter would perfectly pass frequencies below 20 kHz (without attenuating them) and perfectly cut off frequencies above 20 kHz, such an ideal filter is theoretically and practically impossible to implement as it is noncausal, so in practice a transition band is necessary, where frequencies are partly attenuated. In addition, signals must be low-pass filtered before sampling to avoid aliasing. Since human hearing range is roughly 20 Hz to 20,000 Hz, the sampling rate had to be greater than 40 kHz. The Nyquist–Shannon sampling theorem says the sampling frequency must be greater than twice the maximum frequency one wishes to reproduce. The technical reasoning behind the rate being chosen is associated with characteristics of human hearing and early digital audio recording systems as described below. Ultimately Sony prevailed on both sample rate (44.1 kHz) and bit depth (16 bits per sample, rather than 14 bits per sample). The actual choice of rate was the point of some debate, with other alternatives including 44.1 / 1.001 ≈ 44.056 kHz (corresponding to the NTSC color field rate of 60 / 1.001 = 59.94 Hz) or approximately 44 kHz, proposed by Philips. The rate was chosen following debate between manufacturers, notably Sony and Philips, and its implementation by Sony, yielding a de facto standard. The exact sampling rate of 44.1 kHz was inherited from PCM adaptors which was the most affordable way to transfer data from the recording studio to the CD manufacturer at the time the CD specification was being developed. The Nyquist–Shannon sampling theorem states that a sampling rate of more than twice the maximum frequency of the signal to be recorded is needed, resulting in a required rate of at least 40 kHz. The selection of the sample rate was based primarily on the need to reproduce the audible frequency range of 20–20,000 Hz (20 kHz). This sampling frequency is commonly used for MP3 and other consumer audio file formats which were originally created from material ripped from compact discs. Its use has continued as an option in 1990s standards such as the DVD, and in 2000s, standards such as HDMI. This then became the basis for Compact Disc Digital Audio (CD-DA), defined in the Red Book standard in 1980. The 44.1 kHz sampling rate originated in the late 1970s with PCM adaptors, which recorded digital audio on video cassettes, notably the Sony PCM-1600 introduced in 1979 and carried forward in subsequent models in this series. Early digital audio was recorded on U-matic video cassette tapes. ![]()
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