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Od: 2013-10-18
| What is Bandwidth? (Bandwidth and Signal Processing)
Throughout this lecture, we use an Analog Arts (http://analogarts.com/) SF880 for signal analysis.
In analog signal processing, bandwidth is the difference between two frequencies at the lower and upper boundaries of a continuous set. It is typically quantified in hertz. Ideally, a signal with a frequency that lies in the specified range passes through a medium without a significant amount of amplitude reduction. On the other hand, frequencies outside the bandwidth range, experience an amplitude loss. Generally, the amplitude reduction is specified in dB. Most often, bandwidth specifies the frequency at which the processing loss is 3 dB or about 30 percent of the input signal.
Base-band and pass-band terminologies describe the lower frequency boundary for a given bandwidth.
In a Base-band system the lower boundary is 0 Hertz or DC. And the higher boundary is referred to as the bandwidth of the system.
For a pass-band system, bandwidth defines a frequency range around a mid-point called the center frequency. The two cutoff frequencies are the center frequency plus and minus one half of the bandwidth
In a baseband system, bandwidth defines the 3 dB cut off frequency, whereas in a pass-band application, both the bandwidth and the center frequency are required to determine the frequency response of the system.
A signal is a composition of one or more sine waves. Sine waves of different frequencies, amplitude, and phase are the building blocks of any signal. The difference between the highest and the lowest frequency components define the required bandwidth to process the signal. For example an ideal square wave, regardless of its period is composed of infinite number of frequencies and therefore it ideally needs an infinite processing bandwidth.
To properly process a signal, the required bandwidth should be considerably larger than the highest frequency component of the signal.
The bandwidth of a system depends on several factors and is generally limited by the component with the smallest bandwidth.
Although the detectable frequency range of human ear is 20 Hz to 20 kHz, limiting an audio system to this bandwidth distorts the sound. That is a reason why we can easily distinguish a recorded audio versus a live audio. A higher bandwidth often offers more flexibility. However, at times the bandwidth of a system is intentionally lowered to zoom on a specific band of frequencies or to reduce noise.
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