Slew rate measures an audio device’s ability to accurately reproduce changes in amplitude. A faster slew rate is desirable to avoid distortion, and manufacturers provide guidelines for acceptable frequency ranges. Slew rate is determined by the device’s amplifier capability and can be measured using equipment such as an oscilloscope. Slow slew rates lead to poor sound quality and distortion, but testing can help identify and repair issues.
Slew rate is a term used to identify the efficiency of certain types of audio devices to accurately reproduce changes in amplitude within a given period of time. The idea is to evaluate the rate of change both in terms of strength and continuity, and how much distortion occurs when the sound is reproduced. For the most part, a faster slew rate is desirable, as slower speeds are usually characterized by increasing amounts of sound distortion.
One of the main purposes of determining slew rate is to identify the maximum amount of input frequency that the amplifier can handle without creating distortion at the output. Most manufacturers provide guidelines that identify an acceptable range for frequency when the amplifier generates both low and high frequencies during operation. Consulting these guidelines is important, as the scale or range considered acceptable can vary slightly from one manufacturer to another.
Identifying slew rate requires identifying the capability of the amplifier in terms of how much signal voltage the device is capable of producing. In general, an acceptable speed would be one-tenth of whatever amp rating the device has. For devices equipped with higher amplifiers, the slew rate can be closer to a fifth of that amount if the amplifier is to produce the highest quality sound reproduction.
A slow slew rate leads to distortions in the sounds produced by the amplifier as sound levels change. For listeners, this means that sound quality may suddenly become a bit fuzzy or muffled for some time, or perhaps start drifting in and out if the frequency is unusually low. The end result is that the sound reproduction is of relatively low quality, incomprehensible up to a point, and typically considered unacceptable.
There are several strategies used to measure response speed. Equipment such as an oscilloscope and some type of function generator are often useful for assessing the current state of the frequency. Test equipment only provides speed measurement, but it also provides some clues as to what is causing the distortion in the first place. This is very useful, as the data makes it easier to determine the origin and take the appropriate steps to make repairs. Once repairs are complete, test slew rate a second time to ensure distortion is resolved and amplifier is operating at full capacity.
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