Slides from my AES Reverb presentation

I was invited by the Seattle chapter of the Audio Engineering Society to speak about reverbs and reverb design. I threw together some slides:


Pretty skeletal deck, but it was (hopefully) more entertaining when presented in person. Don Gunn helped me out with a Logic X project that accompanied the presentation. Don also listened to me when I practiced the presentation, and was graceful enough to pretend that he hasn’t heard me ranting on the same topics about 100 times before.

I think I learned more from the people in the audience at the AES presentation than anyone learned from me! It was cool to hear anecdotes from people that had worked at Lexicon and Alesis, as well as folks that had a lot of experience with plate reverbs and echo chambers. Thanks to Christopher Deckard for inviting me to speak, and thanks to everyone that attended the presentation.

A new reverb cartridge for the Z-DSP: Halls of Valhalla

I have been working on code for the Tiptop Audio Z-DSP Eurorack processor for a few years now. I am pleased to finally announce my first product for the Z-DSP, a reverb cartridge called Halls of Valhalla.

The Halls of Valhalla cartridge features 8 original reverberation algorithms, designed to work with the strengths of the Z-DSP, and tailored towards electronic music.

The reverbs in the Halls of Valhalla are arranged in order of perceived size, from small to big to huge to uncomfortably enormous:

  • Room
  • Chamber
  • Plate
  • EnsembleVerb
  • Cathedral
  • Nilfheim
  • Asgard
  • Ginnungagap

Here’s a few sound examples. The first one is a simple 1-osc sawtooth sound, being sent into the EnsembleVerb algorithm. I am adjusting the Mix on the Z-DSP, and the Decay and Chorus parameters on the Halls of Valhalla program:

The next example is guitar, being fed through a B:assmaster fuzz, straight into the Z-DSP, running the Ginnungagap algorithm. The mix is set to 100% wet, and the decay is turned up somewhat.

Halls of Valhalla will be available Q1 2014. Pricing and distribution TBA.

And, yes, I know that the product name is the same name as this blog. IT’S A GOOD NAME.

Valhalla DSP State Of The Union, June 2013

My, how the time flies! We’ve been keeping busy here at Valhalla DSP HQ.

The big news was the release in December 2012 of the latest plugin, ValhallaVintageVerb:

ValhallaVintageVerb1970s ValhallaVintageVerb is a collection of 9 reverb algorithms, inspired by vintage hardware reverbs such as the Lexicon 224/PCM70/300/480L, as well as the EMT250. The GUI continues the “superflat” aesthetic of the earlier Valhalla plugins, with Kristin Costello (my beautiful and talented wife) adding lots of beautiful color and graphic design flourishes to the mix. The parameters have been carefully chosen to balance flexibility with ease of use.

ValhallaVintageVerb has received a great reception so far! Here’s a few reviews:

In other news, I am currently working on the AAX ports of the Valhalla DSP plugins. The main tasks involved are updating my code to use the latest Juce code, and signing the AAX plugins with the Pace Eden copy protection. The progress is a bit slow right now, due to some issues Pace is having with their new copy protection system, so I am waiting for their issues to get resolved to get back on the ports. I’ll be sending out updated versions of the plugins to all users as the AAX ports are finished, as the VST/AudioUnit/RTAS builds will be updated at that time.

Building complex reverbs using ValhallaÜberMod

The original ValhallaÜberMod concept had a fairly sparse Diffusion section, which was intended to smooth out feedback echos and add some density to chorus patches. Somewhere during the development process, the diffusion block was expanded into a much more powerful DIFF section, with each input channel being processed by a dense modulated diffusion block with variable size. The DIFF section proved useful in creating dense nonlinear reverbs, as well as lush ambient reverbs and decent plate simulations. The ÜberMod controls aren’t designed around creating reverbs, so I figured that any reverbs created with ÜberMod were a cool bonus with that plugin.

Flash forward to a few days ago, where I found myself experimenting with ÜberMod, mainly as a way of procrastinating before I get back to work on my next plugin. I started running multiple instances of ValhallaÜberMod in series and parallel, and using the sends of my DAW to control the routing and levels. To my surprise, I found that I was able to create some VERY complex and subtle reverbs using ÜberMod, by allocating different instances of the plugin for different stages of the reverb decay.

EXAMPLE 1: Medium Vocal Reverb, w/early reflections

The first example uses 3 instances of ÜberMod, running on 2 different sends. The first instance is running on its own send, and will cover the early reflections stage of a reverb:

<ValhallaUberMod pluginVersion="1.0.1" presetName="RandomizedEarlyReflections" Mix="1" Depth="1" StereoWidth="0.5" Delay="0.0476999991" Feedback="0" Spread="1" Slope="0.643999994" Skew="0.175999999" Random="1" TapGain="0.5" Diffusion="0.624000013" DiffSize="0.0163265299" DiffModRate="0.0490490496" DiffModDepth="0.5" LowCut="0.0351758786" HighCut="0.232160807" SpatialXover="0.145728648" DetuneRate="0.00900900923" DetuneDepth="0.851999998" VibratoRate="0.298245579" VibratoDepth="0" OverMod="0.0313131325" DriveInGain="0.375" DriveOutGain="0.75" DriveNoiseGain="0.333333343" FeedbackRotate="0.5" SmoothingTime="0.0990990996" ColorMode="1" DelaySync="0" type="0.333333343" DiffEnable="1" Drive="0" DrivePrePost="1" Speed="0" InputPan="0.125"/>

This preset uses the 16Tap mode, in conjunction with the DIFF section, to create a dense early ambience that abruptly cuts off after about 50 to 100 millseconds. The TAP Slope parameter is used to create the perception of a room with a short to medium decay, and the DELAY slider determines the point at which this decay is truncated. Some slow LFO modulation is used in conjunction with the MOD OverMod control to randomize the reflections.

The second instance of ÜberMod is running on a separate send, and provides the input diffusion of the late reverb tail:

<ValhallaUberMod pluginVersion="1.0.1" presetName="InputDiffusion" Mix="1" Depth="0.444000006" StereoWidth="0.5" Delay="0.00999999978" Feedback="0" Spread="0.5" Slope="0.5" Skew="0.5" Random="0" TapGain="0.5" Diffusion="0.703999996" DiffSize="0.0653061196" DiffModRate="0.0130130127" DiffModDepth="0.395999998" LowCut="0" HighCut="0.387939692" SpatialXover="0.145728648" DetuneRate="0.0370370373" DetuneDepth="0.5" VibratoRate="0.298245579" VibratoDepth="0" OverMod="0" DriveInGain="0.375" DriveOutGain="0.75" DriveNoiseGain="0.333333343" FeedbackRotate="1" SmoothingTime="0.0990990996" ColorMode="0" DelaySync="0" type="0.0416666679" DiffEnable="1" Drive="0" DrivePrePost="1" Speed="0" InputPan="0.125"/>

This preset uses the 2TapChorus mode, but most of the work is being done by the DIFF section. A fairly short DIFF size is used, with the idea being to turn impulsive sounds into a “puff” of diffuse energy. This will smooth out any reverb that this preset is placed in front of.

The third instance of ÜberMod is placed in series after the second instance (i.e. on the same send), and generates a reverb tail with a medium decay:

<ValhallaUberMod pluginVersion="1.0.1" presetName="MediumLateReverb" Mix="1" Depth="0.5" StereoWidth="0.5" Delay="0.00999999978" Feedback="0.612999976" Spread="0.5" Slope="0.5" Skew="0.5" Random="0" TapGain="0.5" Diffusion="0.748000026" DiffSize="0.240816325" DiffModRate="0.0290290285" DiffModDepth="0.5" LowCut="0.0954773873" HighCut="0.288442224" SpatialXover="0.145728648" DetuneRate="0.0490490496" DetuneDepth="0.5" VibratoRate="0.298245579" VibratoDepth="0" OverMod="0" DriveInGain="0.375" DriveOutGain="0.75" DriveNoiseGain="0.333333343" FeedbackRotate="1" SmoothingTime="0.0990990996" ColorMode="0" DelaySync="0" type="0.0416666679" DiffEnable="1" Drive="0" DrivePrePost="1" Speed="0" InputPan="0.125"/>

The above late reverb preset also uses the 2TapChorus mode, with most of the work being done by the DIFF section and the FEEDBACK control. The Diffusion is set to a fairly large size. The DIFF Size, in conjunction with the feedback and filtering, determines the length of the reverb decay. The WARP fBMix control is set to 100%, to create a figure-8 (ping-pong) feedback loop, as used in reverbs by Lexicon & Alesis.

Once you have the basic routing set up, experiment with the send levels being sent to the Early Reflections (instance 1) and the Late Reverb (instances 2 and 3). I have found that it sounds best with the Early Reflections set to a somewhat higher level than the Late Reverb.

EXAMPLE 2: Randomized Hall

ValhallaÜberMod is versatile enough that you can emulate many types of reverb structures, not just the Early Reflection / Late Reverb division of the more “scientific” reverbs. For example, Lexicon’s Random Hall is known for its high echo density, and the soft attack derived from the Shape and Spread controls. To emulate this soft attack using ÜberMod, we’ll use 2 instances of ÜberMod in series. The first is used to approximate the Shape/Spread section of Random Hall:

<ValhallaUberMod pluginVersion="1.0.1" presetName="ShapeSpread" Mix="1" Depth="0.444000006" StereoWidth="0.5" Delay="0.342900008" Feedback="0" Spread="1" Slope="0" Skew="1" Random="1" TapGain="0.5" Diffusion="0.791999996" DiffSize="0.134693876" DiffModRate="0.0130130127" DiffModDepth="0.395999998" LowCut="0" HighCut="0.975879371" SpatialXover="0.145728648" DetuneRate="0.0370370373" DetuneDepth="0.5" VibratoRate="0.298245579" VibratoDepth="0" OverMod="0" DriveInGain="0.375" DriveOutGain="0.75" DriveNoiseGain="0.333333343" FeedbackRotate="1" SmoothingTime="0.0990990996" ColorMode="0" DelaySync="0" type="0.375" DiffEnable="1" Drive="0" DrivePrePost="1" Speed="0" InputPan="0.125"/>

This preset uses the 32Tap mode, with a fair amount of Diffusion, and the TAP Slope set to -100%, to create a nonlinear reverb that fades in gradually over time.  The attack time is determined by the DELAY slider.
The ShapeSpread preset is used in series with a 2nd instance of ÜberMod on the same send, that adds a huge reverb tail to the slow attack:

<ValhallaUberMod pluginVersion="1.0.1" presetName="BigLateReverb" Mix="1" Depth="0.760999978" StereoWidth="0.5" Delay="0.00999999978" Feedback="0.768000007" Spread="0.5" Slope="0.5" Skew="0.5" Random="0" TapGain="0.5" Diffusion="0.843999982" DiffSize="0.448979586" DiffModRate="0.0730730742" DiffModDepth="0.495999992" LowCut="0.0502512567" HighCut="0.340703517" SpatialXover="0.145728648" DetuneRate="0.033033032" DetuneDepth="0.5" VibratoRate="0.298245579" VibratoDepth="0" OverMod="0" DriveInGain="0.375" DriveOutGain="0.75" DriveNoiseGain="0.333333343" FeedbackRotate="1" SmoothingTime="0.0990990996" ColorMode="0" DelaySync="0" type="0.0416666679" DiffEnable="1" Drive="0" DrivePrePost="1" Speed="1" InputPan="0.125"/>

This preset is very similar to the earlier late reverb preset, but with a much greater DIFF size setting. In addition, the WARP Speed is set to 1/2, which doubles the size of the diffusors, to create a HUGE reverb decay.


The above examples are just 2 quick demos of the complex reverb responses that can be generated with multiple instances of ValhallaÜberMod. For example, a longer gated reverb could be used in parallel with a reverb that incorporates DRIVE in the feedback loop, to create a reverb that starts off clean, then turns nasty after a certain amount of time.

ÜberMod is also useful in extending the capabilities of other reverb plugins. For example, the InputDiffusion or ShapeSpread examples from above can be used in series with ValhallaRoom, to create a super lush reverb that has more “standardized” reverb controls. The RandomizedEarlyReflections example can be added in parallel to ValhallaShimmer, to add early reflections to the modulated Shimmer late decay. Or combine ÜberMod with any other reverb plugin, algorithmic or convolution, as you see fit.  The low CPU consumption of ÜberMod makes it easy to use it in conjunction with other plugins.

It is worth noting that the same process can be used in the construction of all sorts of complicated sonic events, not just reverbs. ValhallaÜberMod excels at choruses, ensembles, multitap delays, echos, and so forth. By combining different settings of ÜberMod in series and parallel, all sorts of weird and wonderful sounds can emerge. I encourage people to use ÜberMod as a modular building block for creating all sorts of complex effects.

ValhallaRoom Updated to Version 1.1.0

ValhallaRoom has been updated to version 1.1.0.

The latest changes:

  • New reverb mode: LV-426.
    • In keeping with the Nostromo/Narcissus/Sulaco tradition, this is a deep dark space verb. It is kind of a cross between Nostromo and Narcissus, but with a far higher earlier echo density than either of those reverb. LV-426 has a slower attack than the other reverb modes, and a lush, diffuse random modulation that produces beautiful long decays.
    • The LATE LowMult/Xover and LATE HighMult/Xover filters have been moved to a location where they act as tone controls.
    • Values of LowMult less than 1.0 allow you to dial in reverbs with less low frequency energy.
    • The LowXover control can be used to adjust the crossover freq of the low cut/boost.
  • 64-bit VST for OSX. ValhallaRoom is now fully 32 and 64-bit compatible for both Windows and OSX.
  • Optimized CPU for Windows RTAS and VST32
  • Fixed mono->stereo bypass bug in RTAS
  • Window resizing bug fixed in Digital Performer

Update links have been sent to all ValhallaRoom customers, and new demo versions are available for testing at the ValhallaRoom page.

ValhallaUberMod: The Modes

In keeping with the tradition set by ValhallaShimmer and ValhallaRoom, there are several different “modes” in ValhallaÜberMod. These modes are selected by clicking on the name of the currently active mode, to the right of the “MODE:” text. A popup menu will appear, with the names of the available modes:

Each of the ÜberMod Modes selects a specific combination of delay output taps, as well as different modulation options for moving those taps around. I have referred to these as chorus modes or delay modes, but they are really both, so “modes” is probably the best description. A few things that all the Modes have in common:

  • Separate LFOs for slower and faster modulation. The idea is that the slow LFOs are used to create the base “detuning” of the taps, while the fast LFOs are used to add string ensemble vibrato if desired. Of course, the user can use and abuse these controls however they see fit.
  • Each delay tap in a mode is modulated by a unique LFO, or a unique phase from a multiphase LFO. This creates a high degree of aural complexity.
  • The slower LFOs have their overall rate adjusted by MOD SlowRate, and their depth by MOD SlowDepth and MOD OverMod.
  • The faster LFOs have their overall rate adjusted by MOD VibRate, and their depth by MOD VibDepth.
  • True stereo, where left and right inputs feed separate delay buffers.
  • An even number of delay taps, where half the taps are panned to the left, half to the right. The amount of panning is controlled by the DEPTH parameters. The 8Tap mode, for example, has 4 taps panned left, 4 panned right.
  • All modes have a “pay for what you use” approach to CPU usage. The more taps there are, the higher the CPU. ValhallaÜberMod has been programmed using SIMD-optimized vector functions, so it is pretty darned optimized, but the laws of physics dictate that it is cheaper to compute 2 interpolated delay taps than 32 interpolated delay taps.

ValhallaÜberMod Version 1.0.0 ships with nine different delay/modulation modes:

  • 2TapChorus has two modulated delay taps, one for the left input signal, one for the right input signal. The slow tap modulation is derived from a single triangle LFO, with the modulation phase inverted for one of the taps (I call this “antiphase modulation”). The vibrato modulation uses a quadrature oscillator, with the left and right modulations separated by 90 degrees. The 2TapChorus mode is useful for emulating the Roland Dimension C and Dimension D choruses, and also serves as a useful starting point for tape echos, diffusion-based reverbs, and all sorts of other effects.
  • 4TapEnsemble has four modulated delay taps, two for the left input channel, two for the right input channel. There are two slow LFOs, one for the left taps and one for the right taps, using the same antiphase modulation as the 2TapChorus, but with different rates for each channel. Each channel has a single sine vibrato oscillator modulating one of the taps, with different rates for each input/output channel. The 4TapEnsemble can be viewed as 2 mono versions of the 2TapChorus, one panned left, and one panned right. The architecture was derived from the ensemble section of the VP330, and is naturally suited towards creating string ensemble emulations, as well as thick detuned choruses.
  • SuperSix has 6 modulated delay taps (3 left/3 right). There are 3 slow triangle LFOs, using the antiphase modulation technique, with the LFO frequencies staggered to emulate the detuning of the sawtooth oscillators in the JP8000 SuperSaw. Each channel has its own independent 3-phase vibrato LFO (0/120/240 degree outputs), for emulating the vibrato component of classic string ensembles. The vibrato speed is slightly different between left and right channels, for a wider stereo spread. The SuperSix mode is a good starting point for emulating the “unison” control on older analog polyphonic synths, when all of the oscillators were used to create a massive detuned sound. SuperSix is also useful for creating triplet echos, short gated sounds, and other multitap effects.
  • 6TapRandom has 6 modulated delay taps (3 left/3 right), and 3 slow LFOs, each of which has a randomized triangle waveform for the slow LFO. The left and right channels are modulated in antiphase, in a similar manner to the SuperSix mode, but the randomized triangle results in less audible patterns for the detuning. There are 6 independent vibrato LFOs, one for each output tap. The 6TapRandom mode is useful for thick multitap choruses, with less audible patterns than the SuperSix mode.
  • DualEnsemble is a stereo version of the classic string ensemble choruses, as found in the Solina/ARP String Ensemble, Crumar Performer, Moog Opus 3, Korg Polysix, and so on. Each channel has its own dedicated 3-phase slow LFO (0/120/240 degree outputs), with each of the 3 taps per channel being modulated by its own phase. An identical LFO, running at a faster rate, is used for the vibrato modulation of the taps. The 3-phase LFOs for left and right channels are running at slightly different rates, to create the impression of a separate string ensemble for left and right channels. The DualEnsemble mode is the first place to turn for emulating vintage ensembles, but is also useful for creating unique effects that combine ensemble modulation with multitap effects and diffusion. Check out the SolinaVerb preset (in the Reverbs category) for an example that combines ensemble chorusing, diffusion, and feedback, to create a rich modulated reverb that adds complexity to synth pads.
  • 8Tap has 8 modulated delay taps (4 left/4 right). There are 4 slow triangle LFOs, using the antiphase modulation technique, with the frequencies arranged to produce a smooth detuned sound at “sensible” settings, or a cluster of pitches when OverMod is used. There are 8 sine vibrato LFOs, one per each tap, for thick ensemble sounds. The 8Tap mode is useful for creating realistic orchestral choruses, multitap effects, short gated reverbs, ensemble effects that don’t have the distinctive 3-phase modulation patterns, crazy pitched echos (check out the presets in the Pitched folder, which all use the 8Tap mode) and all sorts of cool things.
  • 16Phase is a 16-tap mode (8 taps left, 8 taps right) where all of the taps are modulated by two unique 16-phase sine LFOs, one for the slow modulation, and one for the vibrato. The phases are staggered left-right to get a wider spatial image. This is useful for creating a “super string ensemble” that has the distinctive lushness and artifacts of the old 3-phase string ensembles, only more so. The 16Phase mode is also useful for denser gated and reverse reverbs, nonlinear echos, metallic comb filtering (with the DEPTH set to 0.0), and areas I haven’t had the chance to explore yet.
  • 16Tap is a 16-tap mode (8 taps left, 8 taps right). There are 8 slow triangle LFOs, using the antiphase modulation technique, with the frequencies arranged to produce a smooth distribution of detuned outputs. The triangle LFO phases are inverted between channels, to get a wide spatial image.  There are 16 sine vibrato LFOs, one per each tap, with the frequencies staggered to simulate 16 separate sound sources. The 16Tap mode is useful for lush choruses that have less obvious “string ensemble” artifacts than the 16Phase mode, realistic modeling of large numbers of instruments, gated and reverse reverbs, and strong comb filters.
  • 32Tap is essentially the same as the 16Tap mode, but with double the taps (16 taps left, 16 taps right) . There are 16 slow triangle LFOs, using the antiphase modulation technique, with the frequencies arranged to produce a smooth distribution of detuned outputs. The triangle LFO phases are inverted between channels, to get a wide spatial image.  There are 32 sine vibrato LFOs, one per each tap, with the frequencies staggered to simulate 16 separate sound sources. The main application of the 32Tap mode is for nonlinear, gated and reverse reverbs, where the high tap density can be used in conjunction with the DIFF controls to get dense reverbs without feedback. All sorts of crazy echos and pseudo-reverbs can be made with the 32Tap mode. It is kinda overkill for chorus applications, but turn up the OverMod control and you can get crazy thick pitch shifting for drum reverbs.

ValhallaRoom Updated to 1.0.8. Resizable GUI, new reverb modes

We’ve been working hard here at Valhalla DSP towers [i.e. I’ve been working hard typing in code on my laptop while sitting at the dining room table]. One of the fruits of this labor:

ValhallaRoom has been updated to version 1.0.8. The newest features:

  • Resizable GUI. When ValhallaRoom was first released, I received several complaints that the GUI was too big. Version 1.0.8 has been updated. Now the GUI can get much, much bigger. It can also get smaller, if that is your thing.
  • Two new reverb modes, Nostromo and Narcissus. The new reverb modes both have a sparser initial echo density than most of the ValhallaRoom modes, and take longer to build in echo density. This, combined with the high frequency attenuation, random modulation, and deliberately noisy delay interpolation, can be used to create grainy emulations of vintage reverbs, as well as denser decays that have a wide spatial image.
    • Nostromo is the biggest sounding reverb in ValhallaRoom, with audible echos at the largest size settings that slowly evolve into a rich decay.
    • Narcissus is Nostromo’s little sibling, with an initial denser decay. Narcissus is also the “lightest” reverb mode in ValhallaRoom, with a very low CPU hit.

Simon Stockhausen has some beautiful demos using the new ValhallaRoom reverb modes on his Soundcloud page. The first example uses Stockhausen’s amazing soprano sax playing, processed by Nostromo:

The next example uses Symplant through Narcissus:

The final example utilizes a ring modulated sound from Alchemy, and runs it through Narcissus:

Update links have been sent out to all VRoom customers, and demos of the GUI resizing and new modes can be found on the webpage.