UVI's Thorus XT runs each analog voice through its own modeled BBD delay line, while its digital voices use taps from a shared interpolated delay line. Both engines create chorus by moving short delays and mixing the result back with the source, but the route between those points is very different.
A bucket-brigade device does not store audio as digital numbers. It passes sampled analog charge through a chain of stages under control of a high-frequency clock, and changing that clock changes the delay time. Modulate the clock and the delayed signal bends in pitch, which is the movement you hear as chorus.
Digital chorus can produce the same broad effect without copying the BBD's electrical baggage. A digital delay line can move its read position with interpolation, giving the processor much tighter control over timing, noise, filtering, and repeatability.
Noise creates another problem. BBD stages add hiss and other unwanted residue, so many designs compress the signal before the delay line and expand it afterward. This companding improves the signal-to-noise ratio, yet its timing and ratio can also affect the way the processed signal breathes and moves.
Thorus XT models those surrounding stages instead of treating the BBD as a single dirt knob. Each analog voice gets its own delay line, companding, Sallen-Key anti-alias and reconstruction filtering, component variance, optional hiss, and slow modulation-depth drift.
The detail matters because BBD clock and filter behavior are tied together. Lowering the modeled clock rate changes delay-line resolution, while the filtering around it decides how much high-frequency content survives and how strongly aliasing is suppressed. The darker result is therefore not just generic analog coloration pasted onto a clean chorus.
Clean does not mean static. Speed, depth, voice count, modulation shape, feedback color, crossover, and stereo behavior still change the movement substantially. Digital processing simply gives those changes a more controlled base, so repeated settings can behave with far less unintended drift.
UVI even makes the Quality control mean something different in each engine. In Analog mode it changes the modeled BBD base clock from 1 to 48 kHz. In Digital mode it controls band-limited sample-rate reduction on the chorused portion instead, with anti-aliasing before that reduction and reconstruction afterward.
The distinction is useful when comparing the dual-engine chorus design in Thorus XT. Matching the same speed and depth does not make the engines equivalent because Quality is changing a different part of the signal path in each one.
Thorus XT exposes that difference with its Variance control. Increasing it spreads filter cutoff, resonance, and delay-time offsets between analog voices, while adding slow drift to modulation depth. Two voices set to the same nominal chorus parameters can therefore stop behaving like perfectly matched copies.
The compander can become audible too. UVI lets its response time range from 1 to 50 milliseconds, and very fast tracking can follow low-frequency content closely enough to introduce amplitude modulation. A circuit originally there to fight noise can become part of the motion.
Digital chorus avoids those specific imperfections unless the developer chooses to model or add them. It can still be dark, unstable, noisy, or heavily degraded on purpose, but those traits are design choices rather than unavoidable consequences of moving charge through a clocked analog delay line.
Stereo width is separate from all of this. Thorus XT's Wide mode redistributes modulator phases across channels in either engine, so a wide chorus is not evidence of an analog or digital architecture by itself. You can hold the stereo behavior constant and still hear the signal-path differences underneath.
A bucket-brigade device does not store audio as digital numbers. It passes sampled analog charge through a chain of stages under control of a high-frequency clock, and changing that clock changes the delay time. Modulate the clock and the delayed signal bends in pitch, which is the movement you hear as chorus.
Digital chorus can produce the same broad effect without copying the BBD's electrical baggage. A digital delay line can move its read position with interpolation, giving the processor much tighter control over timing, noise, filtering, and repeatability.
BBD chorus carries its support circuit into the sound
A raw BBD is not a clean little delay hiding inside a pedal. High frequencies normally have to be filtered before the signal reaches the chip to reduce aliasing, then filtered again after the delay line to remove clock energy and smooth the output. Those filters help create the darker top end people often bundle together under the vague word "warmth."Noise creates another problem. BBD stages add hiss and other unwanted residue, so many designs compress the signal before the delay line and expand it afterward. This companding improves the signal-to-noise ratio, yet its timing and ratio can also affect the way the processed signal breathes and moves.
Thorus XT models those surrounding stages instead of treating the BBD as a single dirt knob. Each analog voice gets its own delay line, companding, Sallen-Key anti-alias and reconstruction filtering, component variance, optional hiss, and slow modulation-depth drift.
The detail matters because BBD clock and filter behavior are tied together. Lowering the modeled clock rate changes delay-line resolution, while the filtering around it decides how much high-frequency content survives and how strongly aliasing is suppressed. The darker result is therefore not just generic analog coloration pasted onto a clean chorus.
Digital chorus can stay cleaner without staying boring
Thorus XT's digital engine takes another route. Its voices are interpolated taps from a shared delay line, and there is no compander wrapped around them. The processor can create several moving delay positions without reproducing the noise-reduction stages and component tolerances that belong to the analog model.Clean does not mean static. Speed, depth, voice count, modulation shape, feedback color, crossover, and stereo behavior still change the movement substantially. Digital processing simply gives those changes a more controlled base, so repeated settings can behave with far less unintended drift.
UVI even makes the Quality control mean something different in each engine. In Analog mode it changes the modeled BBD base clock from 1 to 48 kHz. In Digital mode it controls band-limited sample-rate reduction on the chorused portion instead, with anti-aliasing before that reduction and reconstruction afterward.
The distinction is useful when comparing the dual-engine chorus design in Thorus XT. Matching the same speed and depth does not make the engines equivalent because Quality is changing a different part of the signal path in each one.
Analog character comes from several small failures
People often describe BBD chorus as unpredictable, but the useful part is knowing where the variation comes from. Real component tolerances can shift delay times and filter behavior from one voice to another, while clocking, noise, filtering, and gain control introduce limits a digital delay does not need to inherit.Thorus XT exposes that difference with its Variance control. Increasing it spreads filter cutoff, resonance, and delay-time offsets between analog voices, while adding slow drift to modulation depth. Two voices set to the same nominal chorus parameters can therefore stop behaving like perfectly matched copies.
The compander can become audible too. UVI lets its response time range from 1 to 50 milliseconds, and very fast tracking can follow low-frequency content closely enough to introduce amplitude modulation. A circuit originally there to fight noise can become part of the motion.
Digital chorus avoids those specific imperfections unless the developer chooses to model or add them. It can still be dark, unstable, noisy, or heavily degraded on purpose, but those traits are design choices rather than unavoidable consequences of moving charge through a clocked analog delay line.
Stereo width is separate from all of this. Thorus XT's Wide mode redistributes modulator phases across channels in either engine, so a wide chorus is not evidence of an analog or digital architecture by itself. You can hold the stereo behavior constant and still hear the signal-path differences underneath.
