What is Sample rate/Bit depth/sound channel/320kb/CBR/VBR contains in an audio and what's the difference between lossless audio format like wav/ape and loss audio format like mp3/wma？
Many people are wondering if the higher the bit rate, the better the audio quality or if the
lossless audio files truly come with the best sound quality. In the following, we’ll find out.
Let’s start with the audio collection.
Sample rate: it defines the number of audio samples per second captured from a
continuous signal, and it is measured in Hz or kHz.
Bit depth: it determines the dynamic range of the audio collection in bit.
Sound channels: the number of audio channels (1 to 8).
Based on different types of usage, sample rate can be divided into (1 kHz = 1000 Hz):
8 kHz: it is for the equipment like telephone and etc., and is enough for recording human
22.05 kHz: for broadcasts
44.1 kHz: audio CD play
48 kHz: DVD, digital television and etc.
96 kHz – 192 kHz: DVD-Audio, Blu-ray, HD and so on
The common range for bit depth is between 8 bit to 32 bit, and CD uses 16 bit bit-depth.
Saying this, you may be confused that why do many people think 320kb ensures better
sound quality than 128kb file, since the sound quality is not determined by bit rate.
This is because it has audio compression factor involved. Currently, most of the audio
formats are based on the original WAV files of audio CDs. The raw audio data is stored in
an array, and the array is the PCM format. As for WAV format, it is an encoding format
developed by Microsoft, and it is used for encoding and performing PCM format’s data.
WAV can completely restore PCM’ data, besides, other formats like MP3, AAC are based
on WAV file and then compressed. So, we can simply believe that WAV is the original
audio format, and others are compressed formats.
Bit rate is actually the compression ratio, and it defines the file size. In a normal state, the
larger the file, the less the lost data, so it ensures better sound quality. Bit rate itself has no
direct impact on the file quality. For example, we convert a 128kb original file to 320kb, the
new file still won’t offer better sound quality than the 128kb file.
As a result, no all 32kb audio files can ensure better sound quality than 128kb files,
because there are some other factors we have to take into consideration.
So what's the difference between lossless audio format like wav/ape and loss audio
format like mp3/wma？
Compared with lossless audio, lossy audio has lost part of information in order to guarantee
high compression ratio. The lost part mainly refers to high frequency component in lossy audio.
Let’s see a spectrum of lossless audio first.
Then it’s another spectrum of converted mp3.
As a result, we can easily find out that as for mp3, its lost information is mainly related to the
high frequency part.Since lossy audio has lost information about high frequency part, what’s
the difference between lossless audio and lossy audio for common people?
In fact, due to the specific function of our ears, there is almost no difference between the two
audios.The reasons are related to frequency, high frequency and low frequency which can
be shown in the following sentences. I will not explain the physical meaning of the three factors
but to show you with examples.
For instance, when you sing songs in KTV, what’s your feeling of singing Qinghai - Tibet Plateau?
You may fail to achieve the effect of the original one because it’s too high. On the contrary, you
may trouble to get satisfying result by singing the song Rolling east of the Yangtze River because
it’s too low. Why common people always fail to sing the two songs perfectly? For the frequency of
our voice is limited. Meanwhile, it’s the same with our ears. We have learned from the text that the
auditory range of our ears is 20-20kHZ. Conclusions can be drawn according to the spectrum that
ears are not sensitive to high frequency sounds. After a certain level, we will hear nothing. So
common people can hardly distinguish the difference between lossy audio and lossless one.