Audio processing system using delayed audio

• US 5,204,909 A
• Filed: 09/12/1991
• Issued: 04/20/1993
• Est. Priority Date: 09/12/1991
• Status: Expired due to Fees

• Current Assignee: John A. Cowan
• Original Assignee: John A. Cowan
• Inventors: Cowan, John A.
• Primary Examiner(s): Ng, Jin F.
• Assistant Examiner(s): TONG, NINA C
• Application Number:
  US07/758,578
• Time in Patent Office: 586 Days
• Field of Search: 381/110, 381/106, 333/14, 341/132, 328/173
• US Class Current: 381/106
• CPC Class Codes: H03G 3/3005 in amplifiers suitable for low-frequencies, e.g. audio amplifiers H03G3/32, H03G3/34 take precedence
• CPC Class Codes: H03G 7/004 using continuously variable impedance devices

Abstract

An audio processing method is described wherein an audio input signal is delayed and then submitted for signal processing. The signal is sampled prior to the delay and control parameters for speech compression, voice gating, and voice activation of ancillary equipment generated. The delayed audio is then processed according to the parameters determined prior to the delay to eliminate poor transient response and signal clipping.

Claims

1. A method of limiting the peak audio signal level from a signal source of varying levels to a fixed value, using delayed audio to improve transient response, comprising the following steps of:

amplifying the input signal to a suitable level.

sampling the amplified input signal by means of an analog or digital peak level detector wherein the output of said detector rapidly rises to the level of the amplified input signal and slowly decreases as the input level falls,

generating a reference level for signal comparison,

dividing the output of the peak level detector into the reference level by means of an analog or digital divider and thereby calculate a multiplication coefficient suitable for achieving compression of the amplified input signal,

delaying the amplified input signal after the sampling stage by means of an analog or digital delay line for a time interval equal to the cumulative delay introduced by the sampling stage, the divider, and the subsequent multiplier,

multiplying the delayed audio signal by the multiplication coefficient by means of an analog or digital multiplier in a manner so that the peak output of the multiplier will be equal to or less than the reference level,

buffering the output of the multiplier for use by tape recorders, radio transmitters, public address amplifiers or any other equipment requiring an audio input signal.

2. An improved method of detecting the presence of audio signals from a signal source and using the presence of the audio signals from said source to activate tape recorders, radio transmitters, or other ancillary equipment requiring an audio input signal, that uses a delayed audio signal so that said equipment becomes completely operational before the arrival of the audio signal, comprising the following steps:

amplifying the input audio signal to a suitable level,

generating a reference value,

sampling the amplified input signal by means of an analog or digital peak level detector wherein the output of said detector rapidly rises to the level of the amplified input signal and slowly decreases as the input level falls,

comparing the output of the peak level detector to the reference value by means of an analog or digital threshold detector so that a control signal is generated that immediately activates the ancillary equipment whenever signals above the reference level are present in the amplified input signal,

using an analog or digital delay line to delay the amplified audio signal after the sampling stage, by a time equal to the sum of the time required for threshold detection and the turn on time of the ancillary equipment,

extending the control signal from the threshold detector after cessation of audio input by a time equal to the time delay of the audio delay line and making this control signal available so that the ancillary equipment will continue operation until all audio signals have cleared the delay line,

buffering the audio output of the delay line for use as the audio input of the ancillary equipment.

3. A method of generating a voice gate in an audio channel whereby the output of the channel is muted when no audio is present and switched to full amplification when input audio above a given threshold is detected, using delayed audio so that the gate becomes fully operational before being presented with the audio signal, comprising the following steps of:

amplifying the input signal to a suitable level,

generating a reference level,

sampling the amplified input signal by means of an analog or digital peak level detector wherein the output of said detector rapidly rises to the level of the amplified input signal and slowly decreases as the input level falls,

comparing the output of the peak level detector to the reference level by means of an analog or digital threshold detector so that a control signal is generated whenever signals above the reference level are present in the amplified input signal,

using an analog or digital delay line to delay the amplified audio signal after the sampling stage, by a time equal to the time required for threshold detection,

extending the control signal from the threshold detector after cessation of audio input by a time equal to the time delay of the audio delay line so that the control signal is held active until all audio signals have cleared the delay line and making this signal available for the control of an audio gate,

inserting an analog or digital audio gate in the audio signal path after the delay line, controlled by the extended output of the threshold detector in such a manner that the audio path is interrupted when the threshold detector is inactive,

buffering the audio output of the audio gate for subsequent use by public address amplifiers or any other equipment requiring a voice gated audio input.

4. A method of limiting the peak audio signal level from a signal source of varying levels, and using the presence of said audio signal to activate tape recorders, radio transmitters, public address amplifiers, or any ancillary equipment requiring an audio input signal, and further using the level of said audio signal to abruptly mute the audio channel when the input level falls below a predetermined threshold, using delayed audio to improve transient response and eliminate signal loss comprising the following steps of:

amplifying the input signal to a suitable level,

generating a reference level,

sampling the amplified input signal by means of an analog or digital peak level detector wherein the output of said detector rapidly rises to the level of the amplified input signal and slowly decreases as the input level falls,

dividing the output of the peak level detector into the reference level voltage by means of an analog or digital divider to calculate a multiplication coefficient satisfactory for compression of the input signal,

using an analog or digital delay line to delay the amplified audio signal after the sampling stage, by a time equal to the cumulative delay of all arithmetic steps, and the turn on time of any ancillary equipment,

multiplying the delayed audio signal by the multiplication coefficient by means of an analog or digital multiplier in a manner so that the peak output of the multiplier will be equal to or less than the reference level,

comparing the output of the peak level detector to the reference level by means of an analog or digital threshold detector so that a control signal is generated whenever signals above the reference level are present in the amplified input signal and extending the activation time by an additional time interval equal to the audio delay interval so that this control signal is held on until all signals have cleared the delay line,

making this extended control signal available for the control of ancillary equipment and the audio gate,

inserting an analog or digital audio gate in the audio signal path after the delay line, controlled by the extended output of the threshold detector in such a manner that the audio path is interrupted when the threshold detector is inactive,

buffering the audio output of the audio gate for subsequent use by ancillary equipment.

5. A circuit for limiting the peak audio signal level from an audio signal source of varying levels, and using the presence of said audio signal to activate tape recorders, radio transmitters, public address amplifiers, or any ancillary equipment requiring an audio input signal, and further using the level of said audio signal to abruptly mute the audio channel when the input level falls below a predetermined threshold, using delayed audio to improve transient response and prevent signal loss, the circuit comprising:

an audio amplifier stage,

a peak voltage level detector,

a variable voltage reference source,

a voltage threshold detector having the means to compare the peak voltage to the reference and generate a control signal,

a pulse extender having the means to lengthen the control signal by a variable amount so that this control signal is held on until all signals have cleared the delay line, the thusly lengthened signal being additionally available to operate external equipment,

an analog divider whereby the voltage reference is divided by the peak voltage and an output signal made available,

an analog delay line and associated clocking circuitry for the delay of the input audio signal, said delay interval being adjustable,

an analog multiplier operating on the delayed audio signal and the output of the divider, acting as a variable gain stage for the purpose of audio compression,

an audio gate having the means to interrupt the audio signal path between the multiplier and the output, being controlled by the extended control signal,

an output buffer stage.

6. A circuit according to claim 5, where the audio gate is a field effect transistor.