Audio signal monitoring system with display of two signal characteristics

An indicating instrument for displaying characteristics of an audio frequency signal subject to variation in amplitude comprising:

• high impedance input means for producing a voltage signal varying in voltage in proportion to the amplitude variations of said audio frequency signal;
• a meter including an operating movement and indicating means movable in response thereto;
• a display device including said indicating means and a plurality of light emitting diodes located so as to be simultaniously viewable;
• a peak detector and a sample and hold circuit responsive to variations in said voltage signal for energizing said meter to cause the indicating means to instantaneously respond to peak amplitude variations of said voltage signal and provide an indication of integrated energy level thereof;
• and
• circuit means responsive to said voltage signal for actuating selected ones of said light emitting diodes upon said voltage signal attaining different corresponding predetermined amplitude levels for a predetermined period of time.

An audio signal amplitude monitor comprising:

• a high impedance input circuit responsive to an audio input signal for producing a unity gain signal;
• a circuit responsive to said unity gain signal for producing a d.c. signal proportional to the amplitude of said audio input signal;
• a meter movement driver circuit responsive to said d.c. signal for producing a driver signal having a level which instantaneously corresponds to peaks in said d.c. signal and corresponds to a predetermined fall back rate when said d.c. signal falls below said peaks;
• a meter responsive to said driver signal for indicating the instantaneous peak level of said monitored audio input signal and for indicating an integration of the audio input signal energy in accordance with said predetermined fall back rate when said monitored audio input signal falls below said peaks;
• a threshold level circuit responsive to said d.c. signal being maintained at at least one predetermined threshold level for a predetermined time period for producing a corresponding energization signal;
• and
• a corresponding threshold level indicator responsive to said energization signal for producing a visual indication corresponding to the amplitude of said monitored audio input signal exceeding said threshold level for said predetermined time period.

A system for monitoring audio signals comprising:

• means for receiving and precision rectifying an audio signal for producing a d.c. signal output varying in amplitude in proportion to the amplitude of the audio input signal,
• means for peak detecting the d.c. signal output and producing a peak detected output signal representative of instantaneous amplitude peaks of the audio input signal, said peak detecting means producing a slow fall-off of said peak detected output signal following detection of an instantaneous peak of the audio input signal,
• a meter having a scale of values corresponding to amplitude levels of the audio signal and movable indicator means for indicating a value on said scale, said meter being responsive to said peak detected output signal for moving said movable indicator relative to said scale to provide an indication on said scale of the instantaneous amplitude peaks of the audio input signal, said slow fall-off of said peak detected output signal thereby providing an indication of the integrated signal energy of the audio input signal,
• means for supplying a plurality of predetermined threshold level signals,
• comparator means for comparing the level of said d.c. output signal when sustained for at least a predetermined time period with said plurality of predetermined threshold level signals for producing a threshold comparator output signal respectively associated with the predetermined threshold level signal exceeded by said d.c. output signal, and
• said meter further including plural threshold level indicating means respectively corresponding to said predetermined threshold level signals and selectively energized in response to the respectively associated threshold comparator output signals for indicating the level of sustained peaks of the audio signal.