Zisk Multiband Audio Processor

Zisk is a multiband audio processor and player for mobile devices and Raspberry Pi Zero 2 W. Zisk evens out the volume and tonal response of local and remote material in real time, preserving its character while adapting it to a desired sound profile. Gapless playback is achieved through automated volume-based transitions, without perceptible silences,
Zisk processes the audio through various compressors and filters arranged in series and in parallel through a multiband architecture. The signal is processed by an AGC, equalizer, up to 12-band configurable crossover, per-band positive AGC, compression and limiting, bass clipper, stereo widener, bass saturator, final limiter and clipper. In an initial stage, it regulates amplitude so that material with different source levels is perceived at a similar volume (AGC); it then corrects tonal imbalances, attenuating excesses and compensating for deficiencies at certain frequencies; and finally it protects the signal from overshooting and distorting. This processing is especially useful when the material has a wide dynamic range, significant tonal variations, or comes from different sources. The goal is to give the whole a sonic coherence without eliminating the identity or distinctive characteristics of each piece of material. The processor operates independently of how the content is organized: it doesn't recognize tracks, playlists, or sources — only a stream of audio samples.
The player supports WAV, FLAC, and MP3 files and is structured around a playback queue: every track must be added to a queue before it can be played. This queue can include files stored locally on the device or hosted at a remote location accessible via an SMB (Server Message Block) server. The player is designed for extended, unattended listening sessions, especially in vehicles, during sports activities, or in any situation requiring continuous playback. To offer a radio-like experience, it incorporates an automatic transition system based on volume — not time — that links tracks together with no pauses or perceptible silences.
Zisk can also function as a controller for a Raspberry Pi Zero 2 W on which the audio processing runs. The processed sound can be output via USB, Bluetooth, or an RCA output, the latter if a DAC is available. The Raspberry Pi can receive audio over Bluetooth — in which case output must go through USB or a DAC — or from apps such as BubbleUPnP or mconnect via the UPnP AV/DLNA protocols.