ValhallaShimmer Tips and Tricks: Chorus

ValhallaShimmer was primarily designed as a reverberator. However, it can also get some cool chorus sounds. The Chorus preset is a good place to start. Some general tips:

• Set Size as low as possible. This will keep the reverberant quality to a minimum
• Use one of the smaller reverbMode settings. The Chorus preset uses smallStereo, but mediumStereo can be used for a more diffuse, washy chorus.
• Set Diffusion up around halfway to start with, and go from there. Too high of a Diffusion setting will result in more of a small room sound, but this might be what you are looking for.
• modDepth should be set to about 0.5 for starters, and modRate should be adjusted to taste.
• Note that higher settings of Diffusion result in more pitch change for given settings of modRate/modDepth, so you may want to turn down Diffusion and/or modDepth if things get out of hand.
• The bright colorMode will result in a full-bandwidth chorus signal, while the dark colorMode will be closer to the older BBD based choruses.
• Use highCut to control the overall brightness.
• lowCut can be used to shave away the low frequencies, which can add clarity to a chorused signal.
• Feedback should be left at 0 for standard chorusing. Turning it up with the above settings will result in a very metallic sound, which, again, might be exactly what you are looking for.

ValhallaShimmer Tips and Tricks: Shimmering

ValhallaShimmer was designed to get a variety of big reverb sounds, with the option of adding pitch shifted feedback to the decay. The “Shimmer” in the title refers to the classic shimmer effect, as used by U2, Brian Eno, Daniel Lanois, Coldplay, etc. There are a few presets that ship with ValhallaShimmer which reproduce this effect, but if you want to dial in your own version, here’s some tips:

• Use the mediumStereo or bigStereo reverb modes for the smoothest shimmer sounds. The mono reverb mode will have a stronger sense of pitch shifting in the feedback signal, while the other modes have a gentler onset of the pitch shifting.
• Set the Feedback control for the desired amount of pitch shift in the output signal, and then use the Size control to dial in the decay.
• The Pitch control should be at +12 semitones.
• Diffusion works best at around 0.9 for reverberant sounds. If you set Diffusion < 0.5, it will sound closer to a pitch shifted echo, which is another cool sound.
• The different pitch shift modes have different levels of “smoothness”:
  • The single and dual pitch shift modes have more noisiness in their decay. This is better for emulating the orchestral sounds as heard in “Deep Blue Day.”
  • The singleReverse and dualReverse pitch shift modes are much smoother, and are better for organ-esque sounds.
• colorMode should be set to dark. This produces a natural roll-off of high frequencies, which eliminates almost all of the aliasing noise in the feedback path of the pitch shifter.
• Set the modDepth control to a fairly low value at first, as the pitch shifting provides its own random modulation to the signal.

ValhallaShimmer Tips and Tricks: Bloom

The Alesis Midiverb II featured a unique reverb algorithm, which Keith Barr labeled “Bloom.” From the Midiverb II manual:

Programs 45 and 49 are extraordinary variations on the reverse reverb theme. They are exclusive Alesis programs that are unobtainable in any affordable signal processors other than MV II. They are named Bloom and have an envelope that rises (blooms) to a rich and highly diffuse reverb with a smooth decay. These are the ultimate for ethereal effects and long, slow introspective musical passages.

The architecture of ValhallaShimmer lends itself nicely towards emulating the Bloom algorithms of the Midiverb II. A screenshot of the settings:

The key to the emulation is to combine Diffusion of 0.5 with a fairly high feedback setting, and use the reverb mode and size control to tune the attack time of the reverb.

• In the above example, the mediumStereo mode is being used, as it has a fairly lengthy attack with this diffusion setting. This will sound the closest to the original Midiverb II Bloom algorithms.
• The bigStereo mode can give you super long attacks, as will the mono mode.
• The smallStereo mode doesn’t have enough density to get this effect – it will sound like a diffuse echo with a Diffusion setting of 0.5.

The Midiverb II Bloom algorithms didn’t use modulated delays, probably due to cost restrictions of the hardware. Adding modulation to the above settings results in a beautiful, washy soundscape, that works well for ambient synthesizer and guitar.

Keith Barr talked about using allpass coefficients of 0.5 in the original Midiverb (due to this being an easy value to get with bit shifts), and that people complained about the reverb taking too long to build. My guess is that Barr created the Bloom algorithms for the Midiverb II in order to take advantage of this “flaw.” Apparently My Bloody Valentine used the Bloom patches a lot – recent photos of Kevin Shields’ rig show two Midiverb IIs in there.

ValhallaShimmer released for Windows RTAS

I just released the Windows RTAS version of ValhallaShimmer. Set your browsers to

http://www.valhalladsp.com/shimmer.html

and check it out. Demo versions available at that link.

To sum up (as there has been several updates in the last few days): ValhallaShimmer is now released for:

OSX VST
OSX Audio Unit (32-bits)
OSX Audio Unit (64-bits)
OSX RTAS

Windows VST (32-bit)
Windows VST (64-bit)
Windows RTAS

I’m going to go out and enjoy the snow with the kids for the rest of the day (it’s snowing here in Seattle, which doesn’t happen in November that much). After that, I will put up a few blog entries about ValhallaShimmer, explaining the history of it, how it works, tips and tricks, that sort of thing. I also have a few generic topics that I want to cover, although coding has taken priority over happy creative thoughts for the past several months.

ValhallaShimmer updated to version 1.0.2. 64 bit AU, 64 bit Win VST available.

I’ve just updated ValhallaShimmer to version 1.0.2. The new features:

• 64 bit Audio Unit (in addition to the 32 bit AU)
• 64 bit Windows Vista/7 VST (in addition to the 32 bit VST)
• Improved saving/recall for OSX DAWs
• Internal presets now included in the Windows VSTs

Check it out at http://www.valhalladsp.com/shimmer.html

Next up, finishing the Windows RTAS port. After this is done, I hope to get back to blogging every now and then.

ValhallaShimmer released for OSX AU, VST, RTAS. $50. Demo versions online.

After far too much work, ValhallaShimmer is finally available for sale and demoing:

ValhallaShimmer

OSX users, grab yerself a demo copy and see how you like it. Windows folks, I estimate another week of work and beta testing until the Windows VST/RTAS release.

Some thanks are in order:

• Beta testers. You’ve dealt with far too many revisions, and your input has been invaluable.
• The Audio Damage guys. You gave me credit for my work on Eos, at a time when I had never received any public credit for my consulting gigs.
• My old co-workers at Staccato Systems / Analog Devices. It was like going to school, just getting paid.
• My teachers at University of Washington and CCRMA. It was exactly like going to school, except I was learning really cool stuff. You helped me start off on this crazy journey.
• Bram Wessel and David Hopper, for encouraging me to keep going on Shimmer even when I was ready to walk away from the project.
• All of you who have been following this blog and the forums, and giving me words of encouragement.
• Last and by no means least, my lovely wife Kristin has given me emotional and financial support, time, and has been an awesome web designer. Plus, you’ve heard me rant about allpass filters and modulated delays for the past 13 years, which makes you a freaking hero.

Introducing ValhallaShimmer

I am happy to announce my first commercial plugin, ValhallaShimmer:

ValhallaShimmer is an algorithmic reverberation plugin. It is designed to produce BIG sounds, from concert halls, to the Taj Mahal, to the halls of Valhalla.

There are several reverberation modes available, to allow the user to dial in the preferred initial sound. By adjusting the Feedback, Diffusion and Size controls, the attack, sustain and decay of the reverb signal can be fine tuned. The modulation controls can be set to produce subtle mode thickening, glistening string ensemble-esque decays, and the distinctive random modulation of the older Lexicon hall algorithms. Two tone controls and the Color Mode selector allow the timbre to be adjusted from bright and glistening to a more natural dark decay, similar to that produced by air absorption in large spaces.

In addition, ValhallaShimmer has the ability to pitch shift the feedback signal. There are 3 pitch shift modes available:

• Single, where the feedback is shifted up or down by the Shift value.
• Dual, where the feedback is shifted both up and down (in parallel) by the Shift value.
• Bypass, which turns off the pitch shifting (useful for “standard” reverb sounds).

By setting the Shift amount to +12 semitones, and the Feedback to 0.5 or greater, the classic “shimmer” sound is produced, as heard on Eno / Lanois productions for U2 and others. I have discussed the “shimmer” effect in great (excruciating?) detail in earlier blog posts, and applied the research to the architecture of ValhallaShimmer. The resulting algorithms allow for the classic shimmer effects to be generated with ease, as well as a variety of pitch shifted, evolving ambiences.

ValhallaShimmer is the end result of several years of research, and is highly optimized:

• The core pitch shifting algorithm uses randomization to avoid the comb filtering artifacts that can be heard in simpler pitch shifters.
• The code has been optimized for SIMD processors, in order to allow the complex algorithm to run while using a small fraction of modern CPUs.
• The reverberation algorithm has been designed to work in conjunction with the pitch shifting, to allow for high levels of feedback without compromising stability.
• The algorithm works well with cascading multiple instances, both from a signal processing perspective and in terms of the low CPU consumption.

I will be posting more sound examples during the week (earlier examples can be heard here and here). For now, here’s a sound file that showcases the use of ValhallaShimmer for deep ambient sounds. The example uses 4 instances of Shimmer in series, with pitch shifting on 3 of the instances (+/- 12 semitones, +/- 7 semitones, and +/- 5 semitones).

ValhallaShimmer has been released for OSX (AU, VST, RTAS) and Windows (VST). 64-bit Audio Units, 64-bit Windows VST, and Windows RTAS will be coming soon.

Another clip from my upcoming plugin

The following clip shows some of the different modes of my upcoming plugin, ValhallaShimmer:

A brief summary of what is going on:

• The clip begins with harp recorded in a fairly echo free environment
• At 0:24, the mix control on the plugin is set to about halfway. The plugin is currently producing a fairly large reverb sound.
• At 0:48, the feedback control on the plugin is turned up. This results in a much longer reverb sound. It is kinda subtle in this context.
• At 1:13, the Pitch Mode of the plugin is set to “single,” with the pitch shift set at +12 semitones. This produces the classic “shimmer” sound that I have talked about in earlier blog posts, and that featured heavily in Eno / Lanois productions and many classic U2 tracks.
• At 1:38, the harp loop ends, and the “shimmer” reverb decays away. Notice that the reverb increases in pitch as it decays.

In the next few days, I’ll be going into more details about the upcoming plugin. For now, I’m burning the midnight oil in front of the compiler.

Shimmer: Modulation, auto-correlation, and decorrelation

In my previous post, I discussed the Eno/Lanois shimmer sound, and how it is based around a pitch shifter and a digital reverb placed in a global feedback loop. It is worth exploring what is going on in this signal chain at the micro level, and how a fairly simple signal routing can create such a complex sound.

The AMS pitch shifter used by Eno and Lanois used a de-glitching board in its architecture, to find the ideal points for splicing together the time-scaled waveform chunks. This presumably worked in a similar manner to the H949 de-glitching card, in that autocorrelation was used to find the most similar segments of the waveform, and the delay time of one of the channels was adjusted for an ideal splice. It is also possible that the auto-correlation would trigger a new splice, such that the rate between splices was a function of the periodicity of the input signal.

Auto-correlation works well for determining splicing points, assuming that the input signal has a certain degree of correlation. A single sustained guitar note, for example, can have a high auto-correlation factor after the initial attack. But what happens when the signal to be shifted has a very low auto-correlation factor? Such a signal is said to be decorrelated; that is, the auto-correlation or cross-correlation is said to be greatly reduced compared to the original signal.

In the audio world, decorrelation often refers to randomization of the phases of the signal while preserving the frequencies, or to a time-varying process to slightly shift the frequencies of a signal to prevent feedback. Both of these processes are present, to a large extent, within time varying reverbs such as the Lexicon 224 and EMT250 used by Eno and Lanois.

The Lexicon 224 Concert Hall algorithm is made up of a number of allpass delays, which preserve the input frequencies while completely scrambling the phase response. In addition, the Concert Hall algorithm uses time varying delays inside of the recursive delay network, which increased the perceived modal density of the reverb, and also impart a beautiful chorusing to the reverb decay. This lushness from time-varying delay lines is very prominent in 1980′s Eno/Lanois productions – in addition to the Concert Hall algorithm and EMT250, they made use of the multi-voice chorus algorithms in the Lexicon units, as well as the Symphonic preset in the Yamaha SPX-90.

So, what happens when a pitch shifter that uses auto-correlation to find the ideal splicing points is put into a feedback loop with a reverb that is highly decorrelated and time-varying? The answer: chaos. The pitch shifter will NOT be able to find ideal splicing points, as the phase of the reverb output is continually being scrambled.

The pitch shifter HAS to splice, whether or not it is a perfect situation, so it will pick the best possible match, but this will probably be a fairly random location each time. The result will be random delays for each new splicing point, or random sizing of the grain windows, depending on how the auto-correlation is used within the pitch shifter. This randomization will cause the sidebands of the input signal to be spread out, such that an individual sinusoid would be turned into a band of frequencies centered around the original (that has been shifted up by an octave).

Add in the additional octaves produced by the feedback, the random sideband spread caused by the modulation within the reverb, and harmonics that are created by analog nonlinearities in the feedback path, and the result is a HUGE amount of sonic complexity generated from a simple system. Put a sine wave into this type of feedback system, and the output can approach near orchestral levels of thickness.

In this light, it is interesting to think about Eno’s use of the DX7 around this time. The DX7 can produce chaotic sounds through the use of cascaded FM, but it can also produce gentle, minimalist textures through the use of parallel operators (sine oscillators). A simple DX7 patch with several parallel sine oscillators and a low FM index may produce a fairly boring sound on its own, but would create an enormous yet controllable sound when fed into a complex feedback loop of digital processing.

Coming up: more on the topic of generating complexity through simple systems with feedback applied to them, both from a technical and creative perspective.

Eno/Lanois Shimmer Sound: How it is made

The basic foundation of the Brian Eno / Daniel Lanois shimmer sound is fairly simple: Create a feedback loop, incorporating a pitch shifter set to +1 octave, and a reverb with a fairly long decay time. By controlling the gain and equalization of the feedback loop, and the lengths of the various delays within the loop, the temporal evolution of the sound can be altered from steel drum-esque sounds to the slow attack “string pads” hear on many of the Eno/Lanois tracks. This is the same technique used by ValhallaShimmer, with the reverberation, pitch shifting and feedback all incorporated within the same plugin.

Kevin Killen, answering a question about the signal flow on the U2 song “4th of July” on Gearslutz, described the signal path as follows:

The delay and modulation was derived from the AMS 1580. On its fader return , some hi frequencies were rolled off, then it was fed into a 224 Hall setting, probably 5 seconds but with a rolloff in the top and bottom. This return may have been equalised also. We may have added a second delay but then the delays have to be timed to the track as the net effect is blurring the chord progression…Our last tweak would be to play with the sends on all of the returns to the point that its almost recirculating out of control, which in turn is creating a layer upon layer effect.

The AMS DMX 15-80s was a digital delay / sampler / pitch shifter that was in common use in Britain in the early 1980′s. Eno and Lanois have both sung the praises of this unit, and Wendy Carlos has said that the AMS unit had “perhaps the least audible artifacts to pitch shifting available at that time.”

David Kulka has written that the AMS DMX had an optional de-glitch card installed, which worked on a similar principle to the auto-correlation deglitcher in the H949. His post is worth quoting:

Harmonizers, at least the early ones, had to electronically “splice” sections of the waveform in order to accomplish pitch change. When the out and in points had different voltage levels, a small DC pop could be heard at each transition. The result was a sort of low level crackle, more obvious with certain kinds of program material, and more audible at extreme pitch change settings.

The Eventide H910 exhibited this, along with the early AMS Harmonizers. Both Eventide (on the H949) and AMS partially resolved this by adding “de-glitch” cards. The circuitry on this card added a “smart” algorithm to pitch change, adjusting the transitions to better match voltages at the in and out points.

The “224 Hall setting” that Killen refers to is the Concert Hall algorithm in the Lexicon 224. This algorithm has a fairly low initial echo density, that builds to a higher density as the decay evolves. The Concert Hall algorithm is also distinguished by its high degree of modulation. The resulting sound is not a terribly accurate simulation of a real concert hall, but rather a lush and spatially expansive reverb that is still sought after more than 30 years after its introduction.

Other accounts of the “shimmer” sound refer to different reverbs being used, such as the EMT250. In addition, modulated delay lines, such as the Lexicon Prime Time, have been used by Lanois at different times. The common elements always seem to be the pitch shifter, a modulated reverb and/or a modulated delay line, and feedback and equalization generated via an analog mixer. In my next post, I will analyze the contributions of these elements to the shimmer sound, and will discuss how the various components respond in a feedback situation.