3.3.3.2 Pink noise
In addition to white noise, there is also "pink" noise. The human ear does not hear all frequency ranges at the same volume. It hears best around 2000 Hz, that's why white noise sounds somewhat high. We hear considerably worse in the low and high frequency ranges. If you want to create a noise that humans will perceive as an evenly distribution of all frequencies, you have to adapt it to the way we hear, i.e., the low frequencies have to be significantly louder than the middle frequencies. This distribution is called pink noise and can be generated in Pd using the "pink~" object:
핑크노이즈라는 것이 있는데,
사람은 모든 주파수영역을 같은 볼륨으로 다 들을수는없는데. 핑크노이즈 최상은 2000헤르츠 주변, 화이트 노이즈보다 다소 높은...
어쨋거나, 저주차는 중간 주파수보다 좀 많이 크다.
3.3.3.3 DC offset
When using a microphone, the signal will often exhibit a ground current. This is called "DC offset". The result is this waveform:
마이크를 사용할때 신호가 그라운드 전류를 종종 표시할때가 있다. 그것을 DC Offeset이라고 한다.연산증폭기에서의직류오프셋
This offset amounts to an infinitely slow vibration with a frequency that approaches 0. Because it is so low, it can be filtered out with a high-pass filter that is set extremely low:
이 오프셋은 영으로 다가가는 주파수와 같이 무한히 느린 진동수에 까지 도달하게 된다. 왜냐하면 그것이 꽤 낮고, 너무 낮아서 하이패스 필터로 필터링이 안될 정도 그래서 오프셋 필터링 하는 방법 아래
3.3.4 For those especially interested /// 차후에 정리
3.3.4.1 How digital filters work
The 'inner life' of digital filters is complicated. One should, however, have some sort of an idea about how precisely they work: As described in3.1.1.3.1, a sample rate of 44100 Hz is capable of representing a wave with a maximum of 22050 Hz. This wave would have only two points per period:
디지털 필터로서 inner life 는 좀 복잡한데. 샘플레이트 설명했든ㅅ이 44100은 최대 22050 헤르츠의 웨이브 파일을 재현할 수 있다. 이 웨이브는 한 주기에 두 포인트 가지는데.
If you move this wave just one position, i.e., by one sample forwards or backwards, and then add it to the original wave, the result will be that the two waves cancel each other out completely. This shift can be accomplished (in Pd-extended) with "z~".
너가 한 샘플의 이 웨이브의 한 포지션을 앞 뒤로 옮긴다면, 그런다음 그것을 원래 웨이브에 더한다면, 각가 두웨이브를 취소하는 결과가 나올것이다. 이 변환은 Z~로 수행될 수 있다.
Digital filters employ this method of delaying a wave by one sample and then adding it to the original wave to effect cancellation. The "biquad~" object can be used to adjust this by hand. It executes the following differential equation: y(n) = ff1 * w(n) + ff2 * w(n - 1) + ff3 * w(n - 2) with w[n] = x[n] + fb1 * x[n - 1] + fb2 * x[n - 2].
디지털 필터는 하나의 샘플 웨이브를 지연시키는 방법으로 사용된다. 그런 다음 원래 웨이브에 더하면 웨이브가 취소되는 효과가 있다. biguad~ 오브젝트는 이것을 손으로 조절할 수 있도록 사용된다. 그것은 따라오는 미분방정식으로 실행된다.
'n' is the sample position and ff1, ff2, ff3, fb1, and fb2 are freely defined factors. In Pd, "biquad~" then requires five arguments for ff1, ff2, ff3, fb1, and fb2. The syntax is as follows: "biquad~" [fb1] [fb2] [ff1] [ff2] [ff3]. For the case of the wave of 22050 Hz discussed at the beginning of this section, you could also write "biquad~ 0 0 1 1 0". This suppresses high frequencies, especially waves with a frequency of 22050 Hz, which are completely cancelled out. Here is a low-pass filter using "biquad~":
You can use the biquad formula to create many other kinds of filters. For example, the arguments 1.41407 -0.9998 1 -1.41421 1 will make a "band-reject filter". This is the inverse of a band-pass filter; it rejects - i.e., blocks - a certain band of frequencies around a central frequency, in this case 5512.5 Hz. The explanation for this type of calculation would fill an entire book. In Pd-extended there are objects ("band-pass", "equalizer", "highpass", "highshelf", "hlshelf", "lowpass", "lowshelf", "notch") that carry out these calculations. The advantage of the biquad filter is that considerably steeper filter profiles are possible than with, say, "lop~", "hip~", or "bp~". The drawback is that it not only suppresses certain frequencies but also significantly intensifies others to the point of "explosion" (you can see in the formula, that the filter works recursively).
With biquad processing you can also see that filters employ phase shifts. That's why, e.g., a "bp~" object isn't simply the inversion of a band-reject filter:
