Audio Signal Peak Indicator

Figure 1 

The circuit has been designed to indicate the peak reading of audio signal as well as the audio overload indication.

Overload will normally occur in any system especially if the gain is increased too far. The overload creates a very unwanted distortion of the signal in a two’s complement system which is caused by the cyclic nature of two’s complement numbers where a negative maximum value is generated by a 1-bit overload of positive maximum value. Essential for controlling the levels in a digital audio surrounding is the use of peak reading meters. By detecting consecutive samples at peak level, the indication of overload in a digital audio meter is performed. The consecutive samples at peak level will be considered as an overload and a single sample at peak level cannot be considered. The number of consecutive samples can be normally set in a digital audio overload indicator. Even though the signal is at maximum level and not over, it is possible that overload indication will occur. Due to the full level low frequency signals, the false overload indication is produced having several consecutive samples at peak level.

In this circuit, the indication of peak level is determined by the production of light from the LED D1. The occasional blinking of the LED does not mean a threat but if it blinks very often, it signifies that the device producing the sound needs to lower the volume. The LED will be triggered upon exceeding the +4 dB level. dB is an abbreviation for decibel which is a logarithmic unit of measurement which specifies the degree of a physical quantity in relation to a specific reference level. 4 dB is sometimes used in the U.S. Air Force devices and is used by most professional designs.

The circuit plays a vital part in every channel of the sound console of any amplifier. During the indication of overload level, a voltage of 1.25 V RMS is produced. In using the circuit with different levels of signal, a trimmer may be applied and placed before the capacitor C1, to make fine adjustments in the circuit. The circuit goes well with the microphone / line balance circuit.

Figure 2 

Sound level meters measure real time sound and can have functions such as signal analysis, noise dose measurement, and different time and frequency weighting. Typical sound level meters are applied in product testing, maintenance inspections and troubleshooting, machine performance analysis, engineering control studies, audiometer analysis and calibration, frequency analysis and calibration, environmental impact studies, community noise assessment, noise ordinance enforcement, environmental noise measurement and compliance, and occupational noise measurement and compliance.

In determining the limits that drive a loudspeaker system, the peak indicator will provide a very useful aid. It will not require any extra power when it is connected directly to the existing wirings of the loudspeaker. It provides reliable means of detection by identifying the very short voltage over swings. A high luminance LED with a diameter of not less than 3 mm is advisable to be used when designing the peak indicator circuit.

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