US 7,548,790 B1 · Effective deployment of temporal noise shaping (TNS) filters

Abstract

In the MPEG2 Advanced Audio Coder (AAC) standard, Temporal Noise Shaping (TNS) is currently implemented by defining one filter for a given frequency band, and then switching to another filter for the adjacent frequency band when the signal structure in the adjacent band is different than the one in the previous band. The AAC standard limits the number of filters used to either one filter for a “short” block or three filters for a “long” block. In cases where the need for additional filters is present but the limit of permissible filters has been reached, the remaining frequency spectra are simply not covered by TNS. This current practice is not an effective way of deploying TNS filters for most audio signals. We propose two solutions to deploy TNS filters in order to get the entire spectrum of the signal into TNS. The first method involves a filter bridging technique and complies with the current AAC standard. The second method involves a filter clustering technique. Although the second method is both more efficient and accurate in capturing the temporal structure of the time signal, it is not AAC standard compliant. Thus, a new syntax for packing filter information derived using the second method for transmission to a receiver is also outlined.

Claims9

Dependent claims

A method of using filters for processing audio signals, comprising:

calculating a filter for each of a plurality of frequency bands;
comparing coefficients of filters in adjacent frequency bands to identify a pair of filters with a shortest Euclidean distance between coefficients;
merging said pair of filters;
repeating all previously recited acts until a predetermined number of total filters is reached;
after said predetermined number of filters is reached, recalculating at least one of said filters using only those frequencies corresponding to a strongest signal within a frequency range covered by said at least one of said filters;
using said recalculated filter for an entire extent of said frequency range;
and
processing audio signals using the merged pair of filters.

5 more elements

A method of using a filter to process audio signals, comprising:

determining a first filter for a first frequency range;
determining a second filter for a second frequency range, said second frequency range including said first frequency range;
calculating a first Euclidean distance between the coefficients of said first filter and a null set of coefficients;
calculating a second Euclidean distance between the coefficients of said first filter and coefficients of said second filter;
calculating a first prediction gain using said first filter;
calculating a second prediction gain between said first filter and said second filter;
if said second Euclidean distance is greater than said first Euclidean distance and said second prediction gain is less than said first prediction gain, then deploying said first filter for said first frequency range and if said second Euclidean distance is not greater than said first Euclidean distance or said second prediction gain is not less than said prediction gain, then:
recalculating the second Euclidean distance between coefficients of said first filter and coefficients of said second filter;
recalculating the second prediction gain between said first filter and said second filter;
redetermining whether the second Euclidean distance is greater than said first Euclidean distance and said second prediction gain is less than said first prediction gain;
and
processing an audio signal using the first filter for the first frequency range.

9 more elements

Dependencies are inferred from the claim text.

Effective deployment of temporal noise shaping (TNS) filters

Life of this patent

Effective deployment of temporal noise shaping (TNS) filters

Life of this patent

Abstract

Claims9