Sampling theorem
It is a very simple explanation, but it can express up to half the sample rate.
When sampling a signal, if the interval is small, it can be restored close to the original signal, but if it is too thick, it cannot be restored (I would like to write a little more detail when talking about signal processing or other time).
44.1 kHz
Why is the rate of 44.1 adopted, which is not well separated? .. ..
Isn’t the technician deliberately wearing a pesky watch to prevent music CDs from being easily copied? I heard something like that. When I searched, it seems this happened (?) Due to the convenience of an old PCM recorder. In this age, it is difficult to know what 44.1 kHz is in development. The 44.1 kHz ↔ 48 kHz sampling conversion is a headache. For example, USB audio (USB audio device class) exchanges data at 1 ms intervals. In the case of 48kHz, the data is 48 samples, but when considering 44.1kHz, it will be 44 samples (x9) and 45 samples (x1) in 10ms. If you cheat on a sample when there are 45 samples (tentatively), it will be 44.0kHz. I think it’s more like that with voice and music, and I think the human ear is mostly misleading (it’s just my personal opinion).
However, with an objective evaluation method, it will soon come to light. For example, you can see that you were clearly fooled by a sine wave (sine wave) (maybe you are unexpectedly on the market).
Number of quantization bits
The sampling had to take a value in the direction of time (discretization), but the quantization had to take a value in the direction of amplitude. The range that it is possible to display the volume of the sound, which is often heard, “96 dB dynamic range” means that the number of quantization bits is 16 bits, and the music signal is played in the range of 0 to 65535. I can do it. The number of quantization bits is also called the bit depth or bit depth.
Bitrate
In communication, it indicates how many bits of data are transferred per hour and is generally expressed in bps (bit / s) of how many bits are transferred (processed) per second. If it is low, the size when saving as a file is small and there is space on the transmission line for communication. For example, when an audio (1 channel) is compressed to 1/3, the 3 channel audio can be sent at the same bit rate. Excuse the old story, but considering the age of analog communication (analog cell phones), digitizing + compression will support multiple calls with the same radio waves.
Finally
I often hear what is called Hi-Res Audio. The sampling frequency is said to be 96 kHz or 192 kHz, which is above 48 kHz, the number of quantization bits is 24 bits, and the limit (high range) of human hearing is about 20 kHz, but it expresses frequencies higher than that. It will be. It is the same bit rate as the image from a long time ago. .. ..
By the way, it seems that dogs can hear up to 60 kHz and cats up to about 64 kHz.
