![\"Audio](\"https:\/\/verdemusicgroup.com\/wp-content\/uploads\/2014\/06\/data-compression.jpg\")
<\/p>\nWhen compressing using audio encoding (AAC, MP3, etc.), the compression rate is determined by the bit rate at the time of encoding.<\/p>\n
<\/p>\n
Specifically, if you set a low bitrate, the compression rate will be high and the file size when saved will be small, but what is the bitrate for the original sound source (PCM) without compression in the first place?<\/p>\n
If you save it as PCM, the sound quality of the original sound will be obtained, but it can be a little inconvenient to save it without worrying about the file size. Also, depending on the application, I think the original sound size has enough memory capacity and the communication speed is correct. Therefore, I would like to write about the sample rate and bit rate that are often heard in digital audio.<\/p>\n
The bit rate of digital audio is determined by the sample rate, the number of bits assigned to a sample (number of quantization bits), and the number of channels (stereo, monaural, etc.).<\/p>\n
PCM bit rate (uncompressed) = sample rate x number of quantization bits x number of channels
\nAs I wrote a bit last time, file containers like wav and mp4 format have this information as the header, so the application can see the header and play it. The compression rate of the encoding is determined by the bit rate specified at the time of encoding for this PCM (uncompressed) bit rate.
\nFor example, as many of you know about music CDs, with 44.1 kHz stereo, this is the next bit rate.<\/p>\n
Music CD bit rate: 44100Hz x 16bit x 2ch (stereo) = 1411.2kbps
\nWhen encoding this with MP3, AAC, etc., you will naturally specify a bitrate less than 1,411.2 kbps. For example, when encoding at 256 kbps, the compression rate is approximately 18% and the file size is 1\/5 or less, assuming the original sound is 100%.<\/p>\n
Encode 256 kbps music CDs: 256 kbps \/ 1,411.2 kbps = approximately 18%
\nGenerally, the sample rates of audio devices actually connected to a PC are 48 kHz and 44.1 kHz for music, 16 kHz and 8 kHz for voice, such as microphones and headphones, and 32 kHz, 24 kHz, 22.05 kHz, etc.<\/p>\n
The bit rate of PCM (uncompressed sound source) with 16-bit quantization bits is as follows.<\/p>\n
Stereo (for music) PCM 16-bit bit rate (example)
\nSampling frequency Number of quantization bits Number of channels bit rate Comments
\n48 kHz 16 2 1,536 kbps
\n44.1 kHz 16 2 1,411.2 kbps Music CD
\n32 kHz 16 2 1,024 kbps
\n24 kHz 16 2 768 kbps
\n22.05 kHz 16 2 705.6 kbps<\/p>\n","protected":false},"excerpt":{"rendered":"