A Typical Digital Signal Processing System
Signal processing is an area of systems engineering, electrical engineering and applied mathematics that deals with operations on or analysis of signals, in either discrete or continuous time, to perform useful operations on those signals. Signals of interest can include sound, images. Signals are analog or digital electrical representations of time-varying or spatial-varying physical quantities.
Electronic filters are electronic circuits which perform signal processing functions, specifically to remove unwanted frequency components from the signal, to enhance wanted ones, or both. Electronic filters can be:
1) passive or active
A passive component, depending on field, may be either a component that consumes (but does not produce) energy, or a component that is incapable of power gain .
An active filter is a type of analog electronic filter, distinguished by the use of one or more active components i.e. voltage amplifiers or buffer amplifiers. Typically this will be a vacuum tube, or solid-state (transistor or operational amplifier).
2) analog or digital
3) high-pass, low-pass, bandpass, band-reject (band reject; notch), or all-pass.
A high-pass filter (HPF) is a device that passes high frequencies and attenuates (i.e., reduces the amplitude of) frequencies lower than its cutoff frequency. A high-pass filter is usually modeled as a linear time-invariant system.
High-pass filters have many uses, such as blocking DC from circuitry sensitive to non-zero average voltages or RF devices. They can also be used in conjunction with a low-pass filter to make a bandpass filter. The actual amount of attenuation for each frequency is a design parameter of the filter.
A low-pass filter is an electronic filter that passes low-frequency signals but attenuates (reduces the amplitude of) signals with frequencies higher than the cutoff frequency. The actual amount of attenuation for each frequency varies from filter to filter. It is sometimes called a high-cut filter, or treble cut filter when used in audio applications. A low-pass filter is the opposite of a high-pass filter.
A band-pass filter is a combination of a low-pass and a high-pass.
Low-pass filters exist in many different forms, including electronic circuits (such as a hiss filter used in audio), anti-aliasing filters for conditioning signals prior to analog-to-digital conversion, digital filters for smoothing sets of data, acoustic barriers, blurring of images, and so on. Low-pass filters provide a smoother form of a signal, removing the short-term fluctuations, and leaving the longer-term trend.
In signal processing, a band-stop filter or band-rejection filter is a filter that passes most frequencies unaltered, but attenuates those in a specific range to very low levels. It is the opposite of a band-pass filter. A notch filter is a band-stop filter with a narrow stopband (high Q factor).
4) discrete-time (sampled) or continuous-time
5) linear or non-linear
6) infinite impulse response (IIR type) or finite impulse response (FIR type)
Infinite impulse response (IIR) is a property of signal processing systems. Systems with this property are known as IIR systems or, when dealing with filter systems, as IIR filters. IIR systems have an impulse response function that is non-zero over an infinite length of time. This is in contrast to finite impulse response (FIR) filters, which have fixed-duration impulse responses. The simplest analog IIR filter is an RC filter made up of a single resistor (R) feeding into a node shared with a single capacitor (C). This filter has an exponential impulse response characterized by an RC time constant.
IIR filters may be implemented as either analog or digital filters. In digital IIR filters, the output feedback is immediately apparent in the equations defining the output.
The most common types of electronic filters are linear filters, regardless of other aspects of their design. See the article on linear filters for details on their design and analysis.
Pitch is an auditory perceptual property that allows the ordering of sounds on a frequency-related scale. Pitches are compared as "higher" and "lower" in the sense associated with musical melodies, which require "sound whose frequency is clear and stable enough to be heard as not noise". Pitch is a major auditory attribute of musical tones, along with duration, loudness, and timbre.
DSP System Needs
Input and output filtering
Analogue to digital, and digital to analogue conversion
Digital Processing Unit
Why Use Digital Processing?
1) Precision - In theory the precision of Digital Signal Processing systems is limited only by the conversion process at input and output.
In practice, sampling rate (sampling frequency) and word length restrictions (number of bits) modify this.
However the increasing operating speed and word length of modern digital logic is allowing many more areas of application.
2) Robustness - Due to logic noise margins, digital systems are inherently less susceptible than analogue systems to: a) electrical noise and b) component tolerance variations.
Adjustments for electrical drift and component ageing are essentially removed; importnat for complex system.
3) Flexibility - Programmability allows upgrading and expansion of the processing operations, without necessarily incurring large scale hardware changes. Practical systems with desired Time Varying and/or Adaptive characteristics can be constructed.
Simple Sound Card Architecture
Sampling a Signal
