Creative Thinking

– Car Audio Normalizer Essay, Research Paper

Project Description and Overview

My proposal for this project is a car audio normalizer. This device would be packaged as a microchip with various input and output pins. The reasons for this device have been experienced by almost everyone with a car audio system of any type.

Weather you own a simple factory made car radio or an expensive custom audio setup, an undesired affect occurs. A desired audio volume is set on the system at some point in time. The problem is that the environmental audio levels almost never stay constant. Typically, an open window, a passing vehicle such as a semi truck, or an increase in engine noise, drowns the audio out. When you manually adjust the audio level back to an audible one, the loud noise may often disappear. The truck passes, or you slow your vehicle, or close your window. After which, the volume level is undesirably high.

My proposed system would be activated when the radio was turned on. Each time the volume is adjusted, the system uses a microphone to sample the environmental audio level and calculate a ratio between the environmental audio level and the audio system volume. Then, using the microphone to sample the environment, the system maintains this ratio by adjusting the audio system volume.


The technology that precedes this device is the heritage of car audio systems. Car audio rose to popularity in the 1950 s when car radios we widely seen in new cars. The first systems that allowed users to play their own music in a car was an eight track system. This was followed by the popularity of the cassette deck in the 1980 s. All these systems are analog, take analog media, and have analog controls, therefore they do not lend themselves to a digital normalizer, which I am proposing.

Modern systems, however, are digital, have digital volume controls, and take digital media. Therefore, a digital normalizer could be used as a component in these systems and would adjust the volume digitally.

There are several similar product patented and possible implemented and on the market. Patent number US5414386 is a muting apparatus for a car audio system. Patent number US5758272 is a patent on a gain controlling system, but it normalizes FM radio signals. There were several graphic equalizers patented, an example being patent number USD0310369. There is also a product on the market that raises the audio system volume in relation to the vehicle s engine rpm s. There are self tuning Dolby Digital 5.1 systems available. A environment audio level controlled system would be a great addition to an already potent arsenal of car audio equipment.

Technical Information and Implementation

The system I have described above would be implemented a microchip and perceivable sold to car audio component manufacturers. This chip would have several inputs and outputs that the manufacturers would have to account for in their system design. The device would include a low pass filter, a microphone input, a DAC, and VLSI circuitry. The block diagram is shown below.

There are several relevant details about the internal circuitry. The first is a low pass filter. This device will cause only low frequency signals to be received from the microphone. This will cause motor sounds, passing vehicle sounds, blowing wind, and the lick to affect the system, but human voices and other high frequency signals will be filter out by the system. In this way human communication does not count as an environmental sound. Humans will be able to talk over the radio, or sing along with it, without having the volume level raise undesirably.

Another feature is the way in which the output volume is adjusted. There will be a setting from system input, that will determine how quickly the volume goes to the new level which maintains the ration of environmental noise to system volume level. Since it is indeterminate weather users would prefer the system to immediately to the new volume level, or gradually adjust the volume. The argument for immediate is that loud distractions may be very temporary and they may be almost over before the system noticeably adjusts. The argument for gradual adjustment is that a fast volume change may be more distracting than beneficial. Again, because the ambiguity, I have chosen to make this a user setting through the audio system.


Environmental audio level changes have long been an annoying drawback to listening to car audio. The solution does not lie in changing the environmental sound levels, but in changing the car s audio system s volume level to match the change in environmental noise. I propose a device that uses a microphone and current volume level input to normalize to a ratio of audio level to environmental noise. This would be packaged as a microchip and sold to car audio component manufactures. It would filter out human speech and be configurable to quickly or slow modulate the output volume level.


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