'audio cd'에 해당되는 글 1건

  1. 2009.03.26 sampling rate 관련 의문 (2)
문득 22KHz로 샘플링된 wav 파일 헤더를 분석하다 의문에 빠졌다.

22KHz라면 현실세계는 1000Hz = 1KHz 니까 22000Hz가 되어야 하는데
실제로 들어 있는 값은 22050Hz 이다. 오잉?

11KHz는 11025Hz
22KHz는 22050Hz
44KHz는 44100Hz

이유? 모른다 -ㅁ-

Although I've mentioned the period as being the duration of one cycle of a sound wave, it is also used to describe the duration of one sample. For example, at 22kHz, the period of each sample is 1/22050s = 0.000045351 seconds (Note that 22kHz rarely equals 22000Hz. A 22kHz sound system would typically run at 22050Hz, and it is only written as 22kHz as a matter of convenience. Similarly 11kHz is 11025Hz and 44kHz is 44100Hz). This means that, every 0.00045351 seconds, the sound hardware reads a sample from the sound buffer, converts it to a voltage, and sends it to the speaker.

[참고 : http://www.iconbar.com/comments/rss/news1209.html]

An audio CD can represent frequencies up to 22.05 kHz, the Nyquist frequency of the 44.1 kHz sample rate.

[출처 : http://en.wikipedia.org/wiki/Red_Book_(audio_CD_standard)]

The audio CD has a specified bandwidth ceiling of 20kHz, leaving a small gap between that upper frequency and half the sampling rate which is 22.05kHz. The filter must be very steep (high order) to remove information above 22.05kHz but still leaving information under 20kHz. Such a filter was developed at the inception of CD playback and was named the "brickwall filter". This filter had a terrible impact on sound quality.

[출처 : http://www.simaudio.com/edu_upsampling.htm]

An audio frequency (abbreviation: AF), or audible frequency is characterized as a periodic vibration whose frequency is audible to the average human. While the range of frequencies that any individual can hear is largely related to environmental factors, the generally accepted standard range of audible frequencies is 20 to 20,000 hertz. Frequencies below 20 Hz can usually be felt rather than heard, assuming the amplitude of the vibration is high enough. Frequencies above 20,000 Hz can sometimes be sensed by young people, but high frequencies are the first to be affected by hearing loss due to age and/or prolonged exposure to very loud noises.

[출처 : http://en.wikipedia.org/wiki/Audio_frequency]

아마도.. 추측성 발언이긴 하지만,
인간의 가청주파수 영역이 20Hz ~ 20000Hz(20KHz) 인데,
다른 주파수와의 gap을 위해 약간의 간격을 더 주어서 22.05kHz를 CD의 기본 주파수로 한 것 같다.
물론 나이키스트 이론(Nyquist Theroy)에 의해서 최대 주파수의 2배로 샘플링을 해야 하므로 44.1kHz가 된 것이고 말이다.

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Posted by 구차니