Thorus XT models a compander with ratios from 2 to 6 and gain-tracking times from 1 to 50 milliseconds. Those controls sit inside its analog BBD path because a bucket-brigade delay has a noise problem before anybody starts worrying about vintage character.
A BBD passes sampled analog charge through a chain of stages, and the useful signal has to share that path with hiss, clock residue, and limited dynamic range. Designers have long used compression before the delay and expansion after it to make the signal survive that trip more cleanly.
The idea sounds like ordinary noise reduction, but the timing matters. Once the gain detector starts reacting quickly enough to bass notes and envelopes, the compander can stop behaving like invisible maintenance and start becoming part of the effect you hear.
After the delay, the expander applies the opposite gain movement. Loud material is restored upward relative to quiet material, while noise introduced between the two stages is pushed down when the expander reduces gain during softer moments.
This is the useful trick behind a BBD noise-control stage. The compressor does not magically remove hiss before it exists, and the expander does not identify noise by frequency. The pair reshapes level around the noisy section so unwanted material added in the middle comes back at a lower relative level.
UVI models the placement quite deliberately. Thorus XT can inject analog hiss after compression inside each modeled delay chain, which means the expander acts on that hiss along with the delayed signal when it performs the return half of the process.
Ratio decides how strongly the level is squeezed and restored. UVI lets you move from 2 to 6, with higher settings deepening the noise-reduction action and making the behavior of the gain detector easier to hear.
Push the response faster, and low-frequency content can begin steering the gain itself. A bass-heavy synth note or guitar signal changes level over each waveform cycle, so a detector that follows closely enough can make the expander move with those cycles.
The result is amplitude modulation rather than simple noise cleanup. Level starts moving in sympathy with the source, adding a subtle pulse or roughness that sits on top of the pitch movement already created by the chorus delay.
This is one reason a compander can color a BBD effect even when its basic job is technical. Attack and release behavior are not neutral once they move into an audible time range, and stronger ratios can make those gain changes easier to notice.
You can hear the difference most clearly when the source has sustained low notes and a steady envelope. Percussive material gives the detector short events to follow, while a held bass note gives fast gain tracking enough time to expose its movement.
Leaving Noise at zero does not make the compander irrelevant. The compressor and expander still alter how the delayed signal passes through the modeled chain, especially once Reactivity becomes fast enough to follow low-frequency movement.
Adding Noise makes the original reason for the circuit easier to hear. Since UVI places the hiss after compression, stronger expansion can push that added noise down during quieter signal periods rather than treating it like noise that existed before the compander.
Higher Ratio settings can make the same Reactivity value feel more obvious because the gain changes become deeper. Faster Reactivity can then shift the character again, trading transparent level control for movement that starts to behave like an extra modulation source.
The crossover adds another wrinkle. Thorus XT high-passes its modeled analog noise at the crossover frequency, so raising the split can keep added hiss out of the low band while the clean bass portion bypasses the chorus path.
A compander therefore has no single sound on its own. Its audible behavior depends on where noise enters, how hard the signal is compressed, how quickly gain follows the source, and what frequencies are allowed through the wet path. In a BBD chorus, those details can shape motion just as clearly as the headline rate and depth controls.
A BBD passes sampled analog charge through a chain of stages, and the useful signal has to share that path with hiss, clock residue, and limited dynamic range. Designers have long used compression before the delay and expansion after it to make the signal survive that trip more cleanly.
The idea sounds like ordinary noise reduction, but the timing matters. Once the gain detector starts reacting quickly enough to bass notes and envelopes, the compander can stop behaving like invisible maintenance and start becoming part of the effect you hear.
Compression gives the BBD more usable signal
The compressor before a BBD reduces the incoming dynamic range, pushing quieter material closer to the level of louder material before it reaches the delay line. This improves the relationship between the wanted signal and noise added inside the BBD path.After the delay, the expander applies the opposite gain movement. Loud material is restored upward relative to quiet material, while noise introduced between the two stages is pushed down when the expander reduces gain during softer moments.
This is the useful trick behind a BBD noise-control stage. The compressor does not magically remove hiss before it exists, and the expander does not identify noise by frequency. The pair reshapes level around the noisy section so unwanted material added in the middle comes back at a lower relative level.
UVI models the placement quite deliberately. Thorus XT can inject analog hiss after compression inside each modeled delay chain, which means the expander acts on that hiss along with the delayed signal when it performs the return half of the process.
Ratio decides how strongly the level is squeezed and restored. UVI lets you move from 2 to 6, with higher settings deepening the noise-reduction action and making the behavior of the gain detector easier to hear.
Fast gain tracking can turn into modulation
Reactivity controls how quickly the compander follows changes in level. Thorus XT spans 1 to 50 milliseconds, and UVI describes slower settings as cleaner and more transparent because the gain movement does not chase every small change in the waveform.Push the response faster, and low-frequency content can begin steering the gain itself. A bass-heavy synth note or guitar signal changes level over each waveform cycle, so a detector that follows closely enough can make the expander move with those cycles.
The result is amplitude modulation rather than simple noise cleanup. Level starts moving in sympathy with the source, adding a subtle pulse or roughness that sits on top of the pitch movement already created by the chorus delay.
This is one reason a compander can color a BBD effect even when its basic job is technical. Attack and release behavior are not neutral once they move into an audible time range, and stronger ratios can make those gain changes easier to notice.
You can hear the difference most clearly when the source has sustained low notes and a steady envelope. Percussive material gives the detector short events to follow, while a held bass note gives fast gain tracking enough time to expose its movement.
Noise, ratio, and reactivity work as one system
The analog chorus engine inside Thorus XT makes this interaction unusually easy to inspect because Noise, Ratio, and Reactivity are separate controls. You can add hiss without changing the compander ratio, then change the detector speed without touching the BBD clock or chorus depth.Leaving Noise at zero does not make the compander irrelevant. The compressor and expander still alter how the delayed signal passes through the modeled chain, especially once Reactivity becomes fast enough to follow low-frequency movement.
Adding Noise makes the original reason for the circuit easier to hear. Since UVI places the hiss after compression, stronger expansion can push that added noise down during quieter signal periods rather than treating it like noise that existed before the compander.
Higher Ratio settings can make the same Reactivity value feel more obvious because the gain changes become deeper. Faster Reactivity can then shift the character again, trading transparent level control for movement that starts to behave like an extra modulation source.
The crossover adds another wrinkle. Thorus XT high-passes its modeled analog noise at the crossover frequency, so raising the split can keep added hiss out of the low band while the clean bass portion bypasses the chorus path.
A compander therefore has no single sound on its own. Its audible behavior depends on where noise enters, how hard the signal is compressed, how quickly gain follows the source, and what frequencies are allowed through the wet path. In a BBD chorus, those details can shape motion just as clearly as the headline rate and depth controls.
