Audio file formats – Understanding the issue of quality


The quality of reproduction for a file format may fairly be assessed by the bit rate without reducing speed, which is the product of the sampling frequency by the number of bits. CD, 44.1 kHz and 16-bit is a kind of pivot in this assessment.

When the flow is reduced, the quality deteriorates rapidly when it increases, it is improving, but less gradually as one moves away.

For live recording, you can not control and anticipate the level, a higher resolution is significant.

Aided by the new computer media, sound can be digitized to 24 bits. This achieves a signal ratio greater than that of the material making the noise.

For mixing and signal processing, it is preferable to use a high resolution to prevent the accumulation of rounding in many calculations that require filters and blends accumulate.

Fast machines allow up to 64 bits (IEEE 754 double-precision), which is probably an excess of caution, and many materials calculate 32 bits (IEEE 754 single precision).

Similarly, increasing the sampling frequency to the sound allows the use of less brutal anti-aliasing filters.

The best filters require a lot of calculation and impose a significant delay to the signal. It is best to leave this for the final phase of production (mastering in music).

Modern appliances offer double sampling and quadruple CD frequencies 88.2 kHz and 176.4 kHz and the TV (48 kHz) or 96 kHz and 192 kHz.

The use of formats is needed for high quality recording and the phases of production. The additional accuracy obtained allows finer calculations during digital processing in audio software.

This provides a subtle quality improvement when applying effects such as reverberation. And the cost is divided between the tens of thousands of consumers of the finished product.

The CD format is governed by different criteria. Each auditor should obtain materials for listening. It must not be too expensive. Registration is not intended to be modified: the level can exploit the full dynamic media and signal processing can hide defects quantification (dither with noise shaping).

The CD, with an effective dynamic approximately 92 dB is adequate for a dynamic sound of 70 dB, corresponding to a mix of classical music. For other genres, it is more than enough, if we judge by the evolution mixes.

It also corresponds to the state of the art in the 1980s, gradually improved by advances in digital filters and dither.

Offers promising superior sound quality available on CD: Physical Disk , DVD- Audio or CD SuperAudio Sony, which has the advantage of being available as a hybrid.

It is both readable by standard CD classic audio on all drives, and a dedicated SACD player.

Format for low-flow evaluation of the sound quality is more complicated. These codecs are trying to recreate the sound impression, and take advantage of the peculiarities of human hearing.

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