# Appendix C. Bit Allocation Pattern

#### (1) About the numeric value

The Bit Allocation Patterns are 32 numeric value required for AHX encoding.

The 32 value settable as the bit allocation patterns mean that:

The number of bit allocated for subbands, where the half of raw audio frequency divided by 32.

In other words, these value specify which subband has a priority over others.

The larger value result in higher audio quality upon playback.

For example, subband width for a raw audio which sampling rate is 48kHz will be:

48000/2/32 = 750 [Hz]

Also, allocation bit patterns have a maximum value for each subband.

The audio quality will not be better if a value larger than max value is specified.

* 0 thru 3 | :maximum value 15
* 4 thru 10 | :maximum value 7
* 11 thru 29 | :maximum value 3
* 30 thru 31 | :maximum value 0

#### (2) How to make the compression rate higher

To get a high compression rate, specify a value as small as possible to the bit allocation pattern. But the smaller value makes audio quality worse. To make the compression rate high while keeping a good audio quality, detailed bit allocation pattern settings are necessary depending on audio contents.

For example, most of the human-voice frequency component consist of 3.5kHz or under.

So by setting a larger value to the component below 3.5kHz where especially important, and smaller values to other less important components, a high compression rate can be achieved while keeping a good quality.

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