fi.helsinki.cs.ohtu.mpeg2.audio.mpa
Class BitAllocator

java.lang.Object
  fi.helsinki.cs.ohtu.mpeg2.audio.mpa.BitAllocator

public class BitAllocator
extends java.lang.Object

Implements a bit allocator for MPEG-1 Layer II audio. The class MP2Encoder uses the the allocator to fit a frame of audio samples to a given number of representation bits. As an output the allocator returns a quantization level for each of the 32 sub-bands.

Before quantization a sub-band sample is (almost) noiseless in respect of representation. Quantization maps the rather precise sub-band samples to a very restricted set of presentation steps. This introduces quantization noise to the samples. The bit allocator tries to 'push' the quantization noise level below the masking level by incrementally increasing the representation precision (also known as bit allocation or quantization level). It does it by increasing the precision on sub-bands that are the most noisy. The total number of representation bits is limited, so the allocation is done once nothing more can be added without overrunning the limit.

Nested Class Summary

static class	BitAllocator.Allocation Represents a bit allocation for a frame of audio samples.
private static class	BitAllocator.SBS State of a sub-band during allocation

Constructor Summary

BitAllocator()

Method Summary

static BitAllocator.Allocation

allocate(QuantizationTables.QuantizationTable qtable, int bitsAvail, int[][] scfsi, double[][] smr) Calculates a bit allocation for a frame with given parameters.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

BitAllocator

public BitAllocator()

Method Detail

allocate

public static BitAllocator.Allocation allocate(QuantizationTables.QuantizationTable qtable,
                                               int bitsAvail,
                                               int[][] scfsi,
                                               double[][] smr)

Calculates a bit allocation for a frame with given parameters.

Parameters:

qtable - the quantization table

bitsAvail - the number of bits available for the allocation

scfsi - the scale factor select information for the frame [subband][3]

smr - the signal-to-mask ratios[channel][subband]

Returns:

an Allocation for the frame