Adaptive Quantization

1. A method of processing audio data, the method comprising:

receiving audio data comprising a plurality of audio objects, the audio objects including audio signals and associated audio object metadata;

determining an importance metric for each of the audio objects, the importance metric being based, at least in part, on an energy metric;

determining a global importance metric for all of the audio objects, the global importance metric being based, at least in part, on a total energy value calculated by summing the energy metric of each of the audio objects;

determining an estimated quantization bit depth and a quantization error for each of the audio objects;

calculating a total noise metric for all of the audio objects, the total noise metric being based, at least in part, on a total quantization error corresponding with the estimated quantization bit depth;

calculating a total signal-to-noise ratio corresponding with the total noise metric and the total energy value; and

determining a final quantization bit depth for each of the audio objects by determining whether the total signal-to-noise ratio is less than or equal to a signal-to-noise ratio threshold; and

if it is determined that the total signal-to-noise ratio exceeds the signal-to-noise ratio threshold, performing the following steps iteratively until it is determined that the total signal-to-noise ratio is less than or equal to the signal-to-noise ratio threshold:

identifying an audio object corresponding with a greatest quantization error;

increasing a bit depth for quantizing the audio object corresponding with the greatest quantization error;

recalculating the total noise metric; and

recalculating the total signal-to-noise ratio,

the method further comprising quantizing the audio signals corresponding to each of the audio objects according to the final quantization bit depths.

2. The method of claim 1 , further comprising:

estimating, for each of the audio objects, an audio object quantization error corresponding to each of a plurality of quantization bit depths;

calculating a total quantization error, for all of the audio objects, corresponding to each of the plurality of quantization bit depths; and

storing, at least temporarily, estimated audio object quantization errors and calculated total quantization errors.

3. The method of claim 1 , wherein the importance metric is based, at least in part, on the audio object metadata.

4. The method of claim 3 , wherein the audio object metadata includes audio object position data and wherein the importance metric is based, at least in part, on the audio object position data.

5. The method of claim 1 , further comprising dithering the audio signals, wherein the total noise metric includes dithering noise.

6. The method of claim 1 , wherein determining the estimated quantization bit depth involves:

determining an energy ratio of each audio object's energy metric to the total energy value; and

determining the estimated quantization bit depth for each audio object according to the energy ratio.

7. The method of claim 1 , wherein the energy metric is a perceptual energy metric that corresponds to human hearing sensitivity as a function of frequency.

8. The method of claim 1 , further comprising sorting the audio objects according to the energy metric of each audio object.

9. The method of claim 1 , wherein the plurality of audio objects corresponds to a single frame of audio data.

10. The method of claim 1 , further comprising outputting quantized audio signals to a lossless encoder.

11. An apparatus, comprising:

an interface system; and

a control system configured to:

receive, via the interface system, audio data comprising a plurality of audio objects, the audio objects including audio signals and associated audio object metadata;

determine an importance metric for each of the audio objects, the importance metric being based, at least in part, on an energy metric;

determine a global importance metric for all of the audio objects, the global importance metric being based, at least in part, on a total energy value calculated by summing the energy metric of each of the audio objects;

determine an estimated quantization bit depth and a quantization error for each of the audio objects;

calculate a total noise metric for all of the audio objects, the total noise metric being based, at least in part, on a total quantization error corresponding with the estimated quantization bit depth;

calculate a total signal-to-noise ratio corresponding with the total noise metric and the total energy value;

determine a final quantization bit depth for each of the audio objects by:

determining whether the total signal-to-noise-ratio is less than or equal to a signal-to-noise ratio threshold; and

if it is determined that the total-signal-to-noise ratio exceeds the signal-to-noise ratio threshold, performing the following steps iteratively until it is determined that the total signal-to-noise ratio is less than or equal to the signal-to-noise ratio threshold:

identifying an audio object corresponding with a greatest quantization error;

increasing a bit depth for quantizing the audio object corresponding with the greatest quantization error;

recalculating the total noise metric; and

recalculating the total signal-to-noise ratio,

the control system further being configured to quantize the audio signals corresponding to each of the audio objects according to the final quantization bit depths.

12. The apparatus of claim 11 , wherein the control system is configured to determine whether the total energy value is non-zero and of determining the estimated quantization bit depth, calculating the total noise metric and calculating the total signal-to-noise ratio only if the total energy value is non-zero.

13. A non-transitory medium having software stored thereon, the software including instructions for controlling one or more devices for:

receiving audio data comprising a plurality of audio objects, the audio objects including audio signals and associated audio object metadata;

determining an importance metric for each of the audio objects, the importance metric being based, at least in part, on an energy metric;

determining a global importance metric for all of the audio objects, the global importance metric being based, at least in part, on a total energy value calculated by summing the energy metric of each of the audio objects;

determining an estimated quantization bit depth and a quantization error for each of the audio objects;

calculating a total noise metric for all of the audio objects, the total noise metric being based, at least in part, on a total quantization error corresponding with the estimated quantization bit depth;

calculating a total signal-to-noise ratio corresponding with the total noise metric and the total energy value; and

determining a final quantization bit depth for each of the audio objects by:

determining whether the total signal-to-noise-ratio is less than or equal to a signal-to-noise ratio threshold; and

if it is determined that the total signal-to-noise ratio exceeds the signal-to-noise ratio threshold, performing the following steps iteratively until it is determined that the total signal-to-noise ratio is less than or equal to the signal-to-noise ratio threshold:

identifying an audio object corresponding with a greatest quantization error;

increasing a bit depth for quantizing the audio object corresponding with the greatest quantization error;

recalculating the total noise metric; and

recalculating the total signal-to-noise ratio,

the software further including instructions for controlling one or more devices for quantizing the audio signals corresponding to each of the audio objects according to the final quantization bit depths.