Frequency used for audio (sample rate, PCM, DSD, etc.)
On this occasion, I would like to explain the frequencies used in digital audio and their meanings.
Recently, the high-resolution sound source has increased, such as 192KHz Toka, 11.2MHz, as the frequency has been written or will, what frequency?
I would like to explain the frequency used for said audio taking as an example the Combo384 installed in the USB-DAC used in LV2.0.
1. 1. What is the sampling frequency?
Music distribution is becoming mainstream these days, but audio was first digitized on CDs, which are still on the market.
You often hear that the sample rate of a CD is 44.1KHz. Since digital signals are basically 0 or 1, to reproduce up to the 20 KHz limit that can be heard by the human ear, a resolution of twice that frequency is required. Furthermore, the frequency was decided to be 44.1 KHz taking into account the digital signal processing margin. Since a musical signal is a set of sine waves, it is 44.1 KHz that can fluctuate at a maximum frequency of 20 KHz.
2. What are 16 bits and 24 bits?
As you may hear often, CDs are sometimes described as 44.1KHz / 16bit. This 16 bit is the volume of the sound. Since 16 bits can express the size of 2 raised to 16, there are 65536 different sizes.
Converting this to dB is 20LOG (65536), which is approximately 96 dB. The dynamic range of a CD (the difference between low and loud sounds) is 96 dB.
For DVD and Hi-Res, it can be 24-bit, but in this case, it’s 16.77 million steps of 144 dB.
3. 3. PCM format
So what is the actual signal? In the case of the PCM format, the standard called I2S, which can support up to 32 bits in sample rate, is common. In the case of a CD, being stereo, the data has a frequency of 44.1 KHz with 2 channels (L, R) alternately 32 bits (although in reality 16 bits are used).
Therefore, to process this digitally, a processing capacity of 44.1KHz x 2CH x 32bit = 2.8224MHz is required.
