Non-professional and easy to understand popular science on sample rate, bit depth, bit rate and lossless – Part 2
Bit rate kbps (kp/s)
In lossless uncompressed formats (such as .wav), bit rate = sample rate x bit depth x number of channels. In lossy compression (for example, .mp3), the bitrate does not equal this formula, because the original information has been destroyed. The bitrate describes the amount of information about the audio in one second, so the total size of the sound file is the bitrate x the total duration. The bit rate is also called the bit rate and the unit is the bit rate (bps, bit per second). Usually 128kbps and 320kbps are bit rates when listening to songs, of which 320kbps is the highest bit rate of mp3 format. But compared to wav file with 44.1 kHz sample rate and 16 bit bit depth (calculate two channel bit rate is 44.1 x 16 x 2 = 1411.2 kbps), it is far from the same. After compression, the bit rate has changed. Bitrate in lossless compression has nothing to do with sound quality, and bitrate in lossy compression is positively correlated with sound quality.
lossless compression
Lossless compression refers to compression (conversion) between formats without loss. Regardless of the format that is compressed (converted), the sound quality is the same and can be restored to the same original file. Lossless generally refers to lossless compression, and there is no such thing as lossless code rate. The compression of various formats corresponds to an algorithm (or encoding), and a decoder is required to decode during playback, and different decoders can also affect the integrity of the decompressed file. Common lossless formats are:
wav – A Microsoft sound file format, which is the closest uncompressed format to real sound (followed by midi), supporting multiple sample rates and multiple quantization precisions. All lossless formats are essentially wav compression, which is converted back to wav when played.
flac: Free Lossless Audio Coded, which is an international general format, characterized by high compression ratio and mature encoding algorithm. When the flac file is damaged, it can still be played normally. Furthermore, this format is also the first lossless format widely supported by hardware.
monkey: The file format converted from CD ripping using Monkey’s audio software, but the advantage is not prominent and decoding is slow.
wma-lossless: It is also produced by Microsoft. It is characterized by a high compression ratio, but it has not become mainstream.
aiff: Produced by Apple, it is the standard audio format on Apple computers.
DSD: I don’t know much about Sony Dafa and I can’t appreciate the spicy culture.
lossy compression
Lossy compression refers to the loss of sound information during the compression process, and the lost sound cannot be represented by the sample rate and number of bits. But the feature is that the compressed file becomes very small and is often used in streaming media. Common lossy formats are:
mp3: A complex algorithm developed to simulate human hearing, known as a “psychoacoustic model”. It improves the compression ratio, lowers the bit rate, and reduces the footprint by extracting some frequency bands in the audio, but at the same time, the details of the sound, such as the emotion of the human voice, the reverberation in the later stage, etc., have been deformed. It is also difficult to distinguish wav and mp3 quickly if you listen blindly and need to use equipment. MP3 is currently the most popular audio compression format, which can best preserve the sound quality before compression.
wma: Microsoft’s masterpiece, characterized by lower bitrate (such as 64kbps), wma can get smaller volume under the same sound quality conditions as mp3. And at ultra-low bit rates (like 16 kbps), wma sound quality is much better than mp3.
aac: The storage format for sound files on Apple computers.
ogg – Completely free, open, and patent-free, but less popular.
