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 number of Hi-Res Audio sources has increased and the frequency is written as 192 KHz or 11.2 MHz. What is this frequency?
I would like to explain the frequency used for such audio taking Combo384 installed on the USB-DAC used in LV2.0 as an example.
1. 1. What is the sample rate?
Music distribution is becoming more widespread 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 44.1 KHz. Since digital signals are basically 0 or 1, reproducing down to the 20 KHz limit that the human ear can hear requires a resolution of twice that frequency. In addition, the frequency was decided to be 44.1 KHz considering the digital signal processing margin. Since a music signal is a set of sine waves, they are 44.1 KHz which can be shaken at a maximum frequency of 20 KHz.
2. What are 16-bit and 24-bit?
As you may often hear, CDs are sometimes described as 44.1KHz/16bit. This 16 bits is the volume of the sound. Since 16 bits can express the size of 2 to the 16th power, there are 65536 sizes.
Converting this to dB is 20LOG (65536), which is approximately 96 dB. The dynamic range of a CD (the difference between soft 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 144 dB.
3. 3. PCM format
So what is the actual signal? In the case of the PCM format, the standard called I2S is common, which can support up to 32 bits in sampling frequency. In the case of a CD, being stereo, the data has a frequency of 44.1KHz with 2 channels (L, R) alternately of 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.
In fact, let’s look at the output of COMBO384.
This is a signal called LRCLK (or FSCLK) where the yellow is changing 2CH (L/R), and a set of LRs are sent every 44.1 KHz.
The blue color below is divided into 32 bits by the DATA line, and the DATA L and R are output.
