Audio Basis - articles about audio
Bit depth is value that defines a number of discrete levels of digital-signal sample. We should distinguish audio and video bit depth. Keep reading for details...
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Sound is an oscillations of air pressure. The intensity of the pressure to ear is changed in time.
The stronger the pressure changes, the louder the sound.
We have an analog signal as air pressure. The analog signal is continuous.
At each instant the intensity has some value.
Measurements of the instant intensity value is stored into computer memory.
Over equal periods, such measuremnents are performed. And the sequence of these measurements into the memory is a digital signal.
The measurement is called "sample". Sample has minimum and maximum values.
The difference between the minimum and maximum is divided into equal shares. Suppose we have N number of the shares.
N is called "quantization level number". It's integer value.
Share = Level quant
In computers, numbers are stored in a memory cell.
The cell contains the number in binary form. It's several bits. Bit is zero or one.
The memory cell has fixed length in bits.
To store the sample in the computer memory the best way, it's suitable:
N = 2m, where,
m is a bit depth or a length of the memory cell in bits.
Bit depth audio point to quantization level number.
You can look at example below.
However, bit depth may point to integer or floating point numbers.
Integer bit depth consists some number bits: 8, 12, 16, 20, 24, 32, 64.
Bit is 0 or 1. Computer memory allows saving number s from -128 to 127 via 8 bits.
One bit is used for sign (plus or minus).
The rest seven bits are used for number:
2 = 0000 0010
1 = 0000 0001
0 = 0000 0000
-1 = 1111 1111
-2 = 1111 1110
127 and -128 is relative numbers that point to maximum signal level for 8 bit resolution.
More number of bits causes lesser noise level. The noise defines precision of digital signal.
Floating point bit depth has range 0.0 ... 1.0
1.0 is highest level of air pressure.
Here is no exact borders between levels. I.e. floating point bit depth provides maximum measurement precision comparing integer ones.
However, it's not applicable for analog-to-digital and digital-to-analog converters.
Float point numbers are stored in computer memory. Standard memory cell for audio applications for float point number may contains 32 or 64 bit.
Bid depth defines quantization noise level. Higher bit depth means lower noise.
There is popular opinion, that 16 bits is enough for highest sound quality.
However, some details are there. Read more...
For different purposes, various bit depths are used:
Speech, lo-fi music - 8 bit
Hi-Fi, Hi-End CD, DVD-video, downloaded audio - 16 bit
Hi-Fi, Hi-End DVD-audio and video, Blue-Ray, downloaded audio - 24 bit
Studio recording and mixing (music production) - 24 or 32 bit and 32 or 64 bit float
For high precision applications - 64 bit integer or floating point
Each pixel (point of monitor or TV screen) has 3 colours.
Each colour has level range of brightness 0 to maximum, that is divided on number levels.
<bit-depth> is number bits in binary number that matches maximum level.
In digital scale for green component of one of TV screen points:
Minimum brighthess is 0.
Maximum brighthess is 255.
255 as a binary number is 11111111. It's 8 bits.
Bit can contain 1 or 0. There are 256 combinations of ones and zeroes for range 0 ... 255.
So, bit depth here is 8 bit.
32-bit depth means that each sample contains 32 bits.
Sample contains information about 1 audio channel. For stereo digital audio signal 1 sample of left channel and 1 sample of right one are united to a frame.
1 second of sounding contains number of frames, that is equal sample rate.