Apparatus and method for maintaining a constant speech envelope using variable coefficient automatic gain control
AssigneeTranscrypt International, Inc.
InventorsSteven P. Poulsen, James P. Preston, II
Life of this patent
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Abstract
An apparatus and method for maintaining a constant speech envelope using automatic gain control, wherein the level of the audio signal is monitored. If increasing, a first level of gain increase is applied to the gain signal. If decreasing, a second level of gain decrease is applied to the gain signal, the second level being less than the first level. By applying a lower level of change to the gain signal when it is seen as decreasing, a more constant speech envelope is obtained during gaps and interstices in the analog signal that are common in speech.
Claims12
A method for maintaining a constant speech envelope using automatic gain control comprising:
- sampling actual audio signal amplitudes;
- computing a running mean on each sample by weighting a previous mean, weighting a current sample and adding the weighted previous mean and weighted current sample;
- using the running mean to alter the current sample;
- selecting the weighting by comparing the amplitude of the current sample with the value of the previous mean;
- if the amplitude of the current sample is larger than the value of the previous mean, weighting the previous mean and current sample more heavily towards the current sample;
- if the amplitude value of the current sample is smaller than the value of the previous mean, weighting the previous mean and current sample more heavily towards the previous mean;
- so that an indication of an increasing signal relative to previous mean results in an automatic gain control level that more rapidly follows the actual signal and an indication of decreasing signal relative to previous mean results in an automatic gain control level that more slowly follows the actual signal.
An apparatus for maintaining a constant speech envelope of an analog signal using variable coefficient automatic gain control (AGC) comprising:
- an input for samples of the analog signal;
- a component to measure the absolute value of the samples;
- a mean generator for calculating the mean of absolute values of samples;
- the mean generator including a component to compute a running mean on each sample by weighting a previous mean, weighting a current sample and adding the weighted previous mean and weighted current sample, a comparator to select the weighting by comparing the amplitude of the current sample with the value of the previous mean and generating a weighting signal;
- if the amplitude of the current sample is larger than the value of the previous mean, the component weighting the previous mean and current sample more heavily towards the current sample;
- if the amplitude value of the current sample is smaller than the value of the previous mean, the component weighting the previous mean and current sample more heavily towards the previous mean;
- so that an indication of an increasing signal relative to previous mean results in an automatic gain control level that more rapidly follows the actual signal and an indication of decreasing signal relative to previous mean results in an automatic gain control level that more slowly follows the actual signal;
- an output for adjusted samples.
Dependencies are inferred from the claim text.