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Radio Design Labs

Articles and Papers

AM Noise Article
A simple definition of AM noise is: unwanted amplitude modulation of an FM carrier. There are two types of AM Noise, synchronous and asynchronous. Asynchronous noise consists of amplitude modulation unrelated to the FM modulation of the carrier, typically caused by power supply hum or vibration. Unless there is a serious problem with the transmitter, asynchronous AM is far less significant than synchronous AM. Unwanted AM modulation produced by normal FM carrier modulation from baseband audio and all subcarriers is synchronous AM, sometimes referred to as incidental AM. Consistent control of synchronous AM noise can result in improved audio clarity, better stereo separation, lower crosstalk into subcarriers and extended service area.
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Basic Distributed Sound Time Alignment
Many distributed Audio systems perform very poorly due to audio timing problems that produce poor intelligibility, muddy sound and a high reverberant field. Audio does not travel as fast through the air as it does through wire. At a listener’s position, the sound from the loudspeakers arrives earlier than the direct sound and the sound of the other loudspeakers. The result is an audio system that sounds bad and is difficult to understand. Read More...

Go For the Gold
RoHS compliance means different things to different people. What’s all the fuss about? Manufacturers that sell products into Europe and other international markets must conform to RoHS, which prohibits electronic products that contain any of several banned substances. The best known is lead, which has been the element in solder that flows between component leads and circuit boards. RoHS compliant products are often referred to as “lead free”. Even if this does not seem relevant to a designer, installer or user of commercial electronic products today, it will become relevant in the future! Read More...

Speed of Sound
Sound travels very slowly in air compared with the speed of light. Light speed is almost instantaneous at 299337 km (186000 miles) per second; sound speed in air crawls along at about 342 meters (1120 feet) per second depending on the temperature. To be exact 343.59 m/s (1127.29 ft/s) at a temperature of 20 degrees C (68 degrees F) and humidity of 60%. It is the relatively slow speed of sound which causes audible echoes to bounce back from a flat surface like a wall, building or mountain. The closer you are to the wall the shorter the echo. As you move further away the echo time lengthens. If you check echo lengths with the chart below, remember to double the length shown because the sound has to travel there and back. Read More...

Increasing Effective Amplifier Output Power Using Audio Compression
The power rating for audio power amplifiers used in commercial installations must deliver the average speech or music power plus reserve power headroom sufficient to handle audio peaks. The average power demanded from an amplifier is only ever a fraction of the total rated power because the average power in either speech or music signals is much less than the peak power. This article examines the relationship between required amplifier power and the dynamic content of speech. Read More...