Also called the Inner Iteration Loop, the Rate Loop adjusts the bit
rate of the data going into the Huffman Coder.

Sometimes the available bits for coding a block of data to the Huffman
Coder exceed the outgoing resulting bits from coding. To correct this,
the rate loop adjusts the Global Gain, creating a larger quantization
step size, in turn, leading to smaller quantized values. This process
is iterated until the demand for bits from the Huffman Coder is small
enough to keep up with the output.