All about Digital Signal Processing

Digital signal processing involves the creation of algorithms designed to mathematically manipulate and enhance real-world signals such as audio, video, pressure, and temperature. Digital signal processors (DSPs), then, are a form of technology that adds, subtracts, divides, and multiplies in rapid fashion to eliminate high-frequency noise from specific parts of the signal. Manufacturers of modern audio products, such as the Apple AirPods Pro and Amazon Echo speakers, utilize DSPs in their hardware.

DSPs are more effective than analog signal processors, in large part due to the differences in value in the latter’s electrical components. Analog circuits require precision for passive and active elements such as resistors, inductors, amplifiers, and capacitors, but this is impossible to achieve for electrical components, meaning analog circuits have limited accuracy. They also aren’t flexible, so hardware needs to be adjusted in order to make changes to a component’s value. DSPs, meanwhile, even allow the transformation of low-pass filters into high-pass filters via the alteration of programmable coefficients.

For audio playback devices, DSPs perform encoding and decoding functions as well as handling user interface, equalization, and volume control. They can also perform tasks associated with active noise cancellation, voice recognition, and bass adjustment.

To illustrate the concept, consider the process of recording and playing files on an MP3 audio player. Analog audio is input through a source during the recording phase and subsequently converted into a digital signal via an analog-to-digital converter. The DSP then encodes the MP3 and saves the file on the device. During playback, the DSP decodes the file, which is then transformed back into an analog signal and outputted through speakers or headphones.

For audio equipment, DSPs are usually small chips that expedite the aforementioned process. However, they can also take the form of larger multi-channel processors used in professional studio equipment and vehicles. A typical DSP contains program memory and data memory in addition to a compute engine and input/output. The compute engine accesses information from the data and program memory and conducts appropriate math processing to perform the desired function.

Although DSPs are core components of modern audio and video technology, manufacturers do not often list DSP capabilities on the spec sheets of their products. For headphones, DSPs are usually paired with the Bluetooth chip. Other devices typically provide speaker driving, digital-to-analog conversion, analog-to-digital conversion, and DSP capabilities on a single chip.

Professional and amateur programmers alike utilize DSPs to develop their own software or perform tasks such as enhancing performance for headphones and bookshelf speakers. After-market DSP boxes can even be used to calibrate virtual surround-sound systems.

There are two distinct categories of digital signal processing. Fixed-point DSPs manipulate integers of at least 16 bits, meaning they can process as many as 65,536 bit patterns. Floating-point DSPs, meanwhile, manipulate rational numbers of at least 32 bits and function similarly to scientific notation. They can yield more than 4.29 million different bit patterns and are therefore more capable of processing data for computationally intensive applications.

Fixed-point DSPs are usually less expensive to produce than floating-point DSPs and are thus used more frequently. However, floating-point DSPs are preferred among designers developing complex algorithms, as they require less manipulation to make up for quantization noise.

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