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How do noise cancelling headphones work? Apple Music review 4 weeks ago. About Us Privacy Policy Contact. Complexity arose in that you cannot simply send the digital data directly to the video recorder. The video recorder was designed only to accept a specific type of waveform called a composite video signal. The most basic version of this video signal type is RS With a bit of a hack, a noninterlaced progressive scanline system can be used, with visible scanlines at 60 FPS.
The signal is monochrome, meaning it is only black and white. You may notice that only the number of horizontal lines vertical resolution is mentioned. RS does not define horizontal resolution, this is simply a product of the frequency bandwidth of your signal basically the maximum frequency that you can have in a signal before something in the system can't handle it.
I also mentioned that only scanlines are visible. A scanline is a single horizontal line on the picture. The 45 invisible scanlines are spent waiting for old CRT TV technology to 'retrace' or move the electron beam back to the top of the screen. Each bit of data is encoded using something known as biphase mark encoding. This basically ensures that there are always signal transitions for the PCM adapter to synchronise to when decoding the video into data. The sony engineers decided on a 14 bit per sample system, with both a left and right channel.
In order for this to work, each channel had to have at least a 40khz sampling rate, with some margin being better. Because of the video bandwidth limit, you could only get so many bits on a line. The sony engineers decided that the visible portion of a line could hold approximately bits using the video tape recorders available at the time. The sony engineers decided to use a whole number of samples per line for the sake of simplicity.
They also wanted to include error correction since the video tape technology wasn't completely reliable we'll talk about error correction later in class. The History of the Hz. Sampling Rate As some of you may know if you have ever messed around with digital audio recording, a common sampling rate for sound is Hz.
Since we are talking about sampling in class right now, I thought it would be interesting to go over the history of this particular sampling rate. As you may or may not know, human hearing caps out at about 20khz or less, depending on gender and age.
They used this rate widely for that moment. In the transition to digital formats, audio were stored in a pseudo-video waveform that could be seen as either black or white representing the binary format.
The field rate and structure used by the television standard is as follows for 60 Hz video: lines per field excluded the first 35 blanked lines. This convention were later used for the CD format, due to equipment compatibility concerns the very first equipment used to produce CD masters used for CD replication was video based.
Source: The Art of Sound Reproduction, p. Since human hearing range is roughly 20 Hz to 20, Hz, the sampling rate had to be greater than 40 kHz. In addition, signals must be low-pass filtered before sampling to avoid aliasing. 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 impossible it is noncausal , so in practice a transition band is necessary, where frequencies are partly attenuated.
The wider this transition band is, the easier and more economical it is to make an anti-aliasing filter. The It seems the hearinig limit for humans might be much higher than 20kHz if looked at from "dynamic" time resolution perspective rather than typical static sinusoidal waves. Also interesting comments about the margin between 20kHz and 22 kHz for reconstruction filtering.
Actually there's been quie interesting work from Peter Craven on time-domain optimized filtering which argues for at least 96kHz for hi-fi playback. A theorem called the Nyquist sampling theorem states that in order to sample a signal of X Hz without significant loss of quality, you need to sample at 2X the frequency.
The limit of human hearing is approximately 20kHz, which hence requires a sample rate of approximately 40Khz. This is why CDs are sampled at 44Khz. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. Why do we choose Ask Question.
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