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LX480 Dual-Engine Reverb

Algorithms – Random Hall

The Random Hall algorithm was introduced on the V4 update of the original hardware in the early 90s.

The Random Hall algorithm is a high-density concert hall reverb algorithm. It gives a smoother reverb tail than a conventional hall algorithm. It’s best for materials that need to sound like they are in a large space or need a longer reverb time, but it can also be used to create higher density smaller spaces.

The Random Hall Algorithm Sound

By the end of the 80s and early 90s, there was a drive to make algorithmic reverbs as real as they could be.

Digital technology had not been able to create the same level of beauty and feeling of being there that you can get from being in a "real" space.

Older reverbs employed chorus-like modulation to reduce metallic ringing in the reverb tail. Random hall was a groundbreaking new approach

One sign that the algorithms were not sounding like real spaces was that low-frequency density was missing from the reverb tail, and early reflections were not authentic.

As technology progressed, digital algorithm design became a balance of science and art.

Just like how perfect, symmetrical real spaces don't sound particularly great for music (due to the reflection patterns being too alike, leading to unpleasant tonal coloration), similar constraints were true for algorithms.

Designers were always looking for new and unique ways to break the predictability of the mathematics of delay loops used to simulate the complexity of real-world scenarios.

The best way to get around the artificial/predictable nature of technological solutions is to add randomness.

Thanks to improvements in computer memory capacity, reverbs gradually become denser. Early pioneers in reverb design suggested a target of 1,000 reflections per second.

By 1989, David Griesenger, the designer of the original hardware suggested that for shortened sounds, this target level be increased to 10,000 per second.

The goal was to design a space digitally that had a lot more flexibility with a lot less of the challenging artifacts of a high-density algorithm

This led to a new approach to algorithm design for the Random Hall, along with a new approach to modulation, with the introduction of the Spin and Wander parameters.

Spin modulates the entire reverberation field at a low rate.

Wander modulates the starting point of each reflection, as well as the time delay between reflections.

Both of these parameters create a much more believable sense of space than anything that had come before.

Key Parameters

Here are a few of the more significant parameters you can use to get the most out of the Random Hall algorithm.

  • Size
  • Shape
  • Spread
  • Spin
  • Wander
  • Early Reflections

Random Hall Algorithm Block Diagram

The following block diagram flowchart is a graphical representation of the steps of the Random Hall algorithm. This makes it easier to understand the logic and flow of the algorithm and its parameters.

Random Hall Algorithm Available Parameters

The following tables lay out all the editable parameters available in the Random Hall algorithm, in both the Hardware Mode and Advanced Mode.

  • Hardware Mode is an authentic reproduction of the original LARC workflow.
  • Advanced Mode gives you a more interactive visual interface, as well as access to additional parameters and functionality. Any additional functionality not available in the original hardware has been highlighted.

 

Hardware Mode

Page Slider 1 Slider 2 Slider 3 Slider 4 Slider 5 Slider 6
Quick Reverb Time Mid (RTM) Shape (SHP) Spread (SPR) Size (SIZ) High Frequency Cutoff (HFC) Pre-Delay (PDL)
Misc Bass Multiply (BAS) Bass Crossover (BXO) High Crossover (HXO) Diffusion (DIF) Reverb Mode (MOD) Mix (MIX)
ERLV Echo Level 1 L > L (LV1) Echo Level 4 R>R (LV4) Echo Level 5 R>L (LV5) Echo Level 2 L>R (LV2) Spin (SPN) Wander (WAN)
ERTM Echo Delay 1 L > L (DL1) Echo Delay 4 R>R (DL4) Echo Delay 5 R>L (DL5)
Echo Delay 2 L>R (DL2)
Reverb Level (LEV)
Den Diffusion (DIF) Decay Optimization Channel (DCC) Decay Optimization (DCO) Reverb Level (LEV) Mix (MIX)
ERTM Echo Delay 1 L > L (DL1) Echo Delay 2 L>R (DL2) Echo Delay 3 L>L (DL3) Echo Delay 4 R>R (DL4) Echo Delay 5 R>L (DL5)
Echo Delay 6 R>R (DL6)
ERVL Echo Level 1 L > L (LV1) Echo Level 2 L>R (LV2) Echo Level 3 L>L (LV3) Echo Level 4 R>R (LV4) Echo Level 5 R>L (LV5)
Echo Level 6 R>R (LV6)

 

Advanced Mode

Page Slider 1 Slider 2 Slider 3 Slider 4 Slider 5 Slider 6
Time Reverb Time Mid (RTM) Bass Multiply (BAS) Bass Crossover (BXO) High Multiply (HIG) High Crossover (HXO)
Reverb Filter Type (RFT)
Shape Shape (SHP) Spread (SPR) Size (SIZ) Pre-Delay (PDL) Width (WID)
Filter Low Frequency Cutoff (LFC) Low Shelf (LOS) High Frequency Cutoff (HFC) High Shelf (HIS)
Output Filter Type (OFT)
Mod Spin (SPN) Wander (WAN)
Den Diffusion (DIF) Reverb Mode (MOD) Reverb Level (LEV) Mix (MIX)
ERTM Echo Delay 1 L > L (DL1) Echo Delay 2 L>R (DL2) Echo Delay 3 L>L (DL3) Echo Delay 4 R>R (DL4) Echo Delay 5 R>L (DL5)
Echo Delay 6 R>R (DL6)
ERVL Echo Level 1 L > L (LV1) Echo Level 2 L>R (LV2) Echo Level 3 L>L (LV3) Echo Level 4 R>R (LV4) Echo Level 5 R>L (LV5)
Echo Level 6 R>R (LV6)

 

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