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Secret of high quality sound. 16 and 24 bit. Part 2


16 and 24 bits

    Now we shall consider size of sample - 16 or 24 bits. They represent accuracy from which measurement of a level of a signal is made. Then more bits - the measurement, the more close discrete (steping) function to the original. At transformation of an analog signal in digital, measurement of a level of a signal is carried out too discretely (in steps). Initial (continuous analog) value is approximated to the nearest integer value of a grid of levels analog-digital converter.

16 bit or 24 bit audio samples

    For example, the grid of levels represents a following range of voltage values:

-5;-4;-3;-2;-1; 0; 1; 2; 3; 4; 5 with step 1V (Volt).

    Measured value let will be equal 3,34V. At analog-digital conversion it gets between values of a levels grid  between 3 and 4 volts. The level 3,34V is rounded to the nearest integer 3V and stored. Restored value of sample is 3V instead of 3,34V (the error of restoration makes 0,34). That also leads to occurrence of distortions.

    And now let the grid the ADC will be twice more exact:

-5;-4,5;-4;-3,5;-3;-2,5;-2;-1,5;-1;-0,5;
0;
0,5; 1; 1,5; 2; 2,5; 3; 3,5; 4; 4,5; 5 Volt.
With step in 0,5V.

    The amount of bits of each sample (measurement) should increase in this case at 1.
Now the initial level 3,34 in gets between values of 3 and 3,5 grids of levels the ADC. The level will be approximated to the nearest value of grid and will accept value 3,5V. Error between the initial and restored signal 3,5-3,34=0,16V (instead of 0,34V at a big step of grid).
These errors generate so-called noise of quantization.

    The amount of bits has special value at digital conversion of silent sounds, even on low frequencies.

Noise of quantization

     It leads to that the form of the signal restored from digital will turn from sine wave in rectangular, with following deterioration of sound, which are not present in analog "smooth" (vinylic or tape) record.
Therefore, for symphonic music which has, both very silent fragments, and very loud, the amount of bits is especially critical. However, other musical genres too much lose from added distortions.

    But it is necessary remember, that vinylic or tape record do bring some distortions in an initial signal. As soon as the acoustic wave passes through the equipment, distortions inevitably correct its form. But about it another time…

    What in future?

    Where the way of improvement of quality of a digital audio record, its approach to analog, and - is even better - to an original acoustic wave? To understand, why so long there lives a format of CD - 44.1 kHz of 16 bits, it is necessary to return to history. This format became the first widely widespread in household audio equipment. It has provided quality of a sound incomparably higher, than the average cassette tape. It has presented convenience of using. Who remembers tiresome fast forwards/rewinds and the heaped up technology of autosearch which are used up the cassette. Has relieved of deterioration the medium of soundtracks (vinyl - it is scratched by a needle, the recorder film - grinds off heads of tape). Frequency of sampling has been chosen from criterion of maintenance of a maximum of quality at approximately hour sounding an album.

    Later, in days of dial-up low-speed modems and USD/Mbyte tariffs of Internet, appeared famous mp3-format. It allowed to compress CD in 10 times, at the decrease of quality appreciable only on the good equipment. The mp3-format is based on reduction of that information and in those places of a soundtrack where this information (for mp3-codec) is not especially significant. But, it leads to the distortions which are not admissible, for "true" sound.

     Now, when unlimited Internet and huge hdd (to measures 10-15 years ago) capacities of steel of nobody in wonder, using of mp3 becomes less obvious. Not including applications in mobile devices. Mp3 is replace with lossless format flac (lossless - compression lost-free qualities).

     CD-format is still alive owing to improbably wide prevalence. But progress, promptly increasing capacity of musical mediums (DVD, two-layer DVD, Blue-Ray, what there further away?), steadily goes to multichannel (5.1 and 7.1) records of quality of 24 bit 192 kHz. And these parameters, similar, too not last limit. Therefore, most likely, in the long term old kind vinyl player will cease to be the sample of softness and heat of sounding. All "vinyl" distortions will simulates by digital processings. Vinyl players will shifted from Hi-End to interiors design of rich apartments and country houses.
 


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