subBands

Subbands are components of a signal obtained by dividing its frequency spectrum into multiple adjacent bands using a filter bank. Each subband contains energy from a specific frequency range, and together they cover the full spectrum. Subbands can be generated with an array of bandpass filters or through polyphase decomposition of a single wideband filter, often arranged as a filter bank. In many designs, the bank is designed so that reconstruction from subbands is possible, sometimes under a constraint of critical sampling.

In digital signal processing, subbands enable processing tasks to operate on narrower portions of the spectrum. For example, noise reduction, equalization, or compression can be performed more efficiently per subband. A synthesis filter bank combines the subbands to reconstruct the original signal; aliasing and phase matching must be controlled to ensure accurate reconstruction.

In audio and multimedia coding, subband coding splits an audio signal into multiple subbands that can be quantized and encoded with different bitrates or perceptual weighting. This can improve compression efficiency and support scalable or progressive transmission.

In communications, subbands are used in multi-carrier systems. OFDM divides the available spectrum into many orthogonal subbands or subcarriers, each carrying independent data streams, while maintaining spectral efficiency and resilience to multipath.

Design considerations include the choice between critically sampled versus oversampled banks, filter selectivity, delay, and the handling of aliasing introduced during analysis and synthesis. Practical implementations often rely on efficient polyphase structures and quadrature mirror filter banks to minimize computational load.