Archive for April, 2012

Looping with Strymon TimeLine

Posted by Ethan

Strymon TimeLine looperHey there! We just put together a couple videos that demonstrate looping with our TimeLine delay.

TimeLine Looper Basics

In this first video, we go over the basic looping features available from the front panel. All you need to do is press and hold TAP to enter looper mode, and you can access Record, Overdub, Play, and Stop. All of your delay knobs and parameters are accessible while looping. You can also set the looper to be pre-delay or post-delay. Running the looper pre-delay allows you to record your dry signal and affect the recorded signal with the delay sounds. Routing the looper post-delay will record the delay sounds to the loop. Check it out:

 

TimeLine Looper MIDI Control

If you want to take your looping a bit further, you can do so by connecting a MIDI controller to your TimeLine. Here we’re using a Voodoo Lab Ground Control Pro, though any MIDI foot controller that can utilize MIDI CC or note messages should work fine. Connecting a MIDI controller will give you access to additional looping features: Reverse, Half Speed, Undo to Initial Loop, Redo, and Looper Pre/Post. In this video, we showcase of these additional features and advanced looping techniques.

 

Setting up your MIDI controller

You can set up your MIDI controller with either MIDI CC (continuous controller), or MIDI note numbers.

MIDI CC values:

Record – CC# 87, any value
Play – CC# 86, any value
Stop – CC# 85, any value
Reverse (toggle) – CC# 94, any value
Full/Half Speed (toggle) – CC# 95, any value
Pre/Post (toggle) – CC# 96, any value
Undo (to initial loop) – CC# 89, any value
Redo – CC# 90, any value
Looper Level – CC# 98, value range 0-17

Note values:

Record – note 0, velocity > 0
Play – note 2, velocity > 0
Stop – note 4, velocity > 0
Reverse (toggle) – note 14, velocity > 0
Full/Half Speed (toggle) – note 16, velocity > 0
Pre/Post (toggle) – note 17, velocity > 0
Undo (to initial loop) – note 7, velocity > 0
Redo – note 9, velocity > 0




Amplifier Tremolo Technology White Paper

Posted by Ethan

Flint Tremolo & ReverbSometimes to understand who you are, you have to go back to the beginning, back to where it all began. Before smart phones, before computers, before integrated circuits and the transistor—the only effects available to guitarists were tremolo and spring reverb. The guitar players of the day didn’t have the rainbow of colors that we have now.

But like a charcoal sketch, there is a stark beauty to the tone without the wash of effects that are now possible. Stripped down to the bare necessities, the contrast of the different tremolos becomes apparent. You feel the beating heart of the photo trem, the rolling waves of the tube trem and the hypnotic swirl of the harmonic tremolo.

Given the storied history of these circuits found within classic amplifiers of the 1960s, there was no doubt that we wanted to develop a studio-class pedal that faithfully delivers three of these iconic and unmistakable tremolo effects. We examined the sonic complexities and tonal interplay, and accounted for every last detail in our hand-crafted algorithms.

The result is the technology found in Flint Tremolo & Reverb. Pete Celi, our Lead DSP Engineer and Sound Designer illustrates the research and sound design process in the White Paper below.

 

Strymon Amplifier Tremolo Technology White Paper

Amplifier Tremolo Overview

Still incorrectly labeled as ‘vibrato’ in many cases, the tremolo effect is a cyclical amplitude (volume) modulation of the input signal. Although there are many cool tremolo effects that can be had by using a simple VCA (voltage-controlled amplifier) circuit and applying geometric waveforms (like sine, triangle, square, ramp) to modulate the amplitude, our interest is in exploring the unique, soothing, pulsing, hypnotic effect that comes out of vintage amplifier tremolo circuits.

There were three main variations that came about in the late ’50s and ’60s. The three types can be referred to as Harmonic Tremolo, Power Tube Tremolo, and Photocell Tremolo. These variations have unique characteristics that result from the very different ways that the effect is achieved

The LFO

One thing that these vintage trem types share in common is the LFO (low frequency oscillator) circuitry, which is generated by a classic positive feedback ‘phase-shift’ oscillator. A network of resistors and capacitors determine the rate of oscillation, and the resultant LFO signal is a mildly distorted sinusoidal signal.

FIG. 1 PHASE-SHIFT OSCILLATOR
FIG. 1 PHASE-SHIFT OSCILLATOR

 

As the LFO circuitry is common to all three trem types under investigation, we can see that LFO waveshape is not responsible for the very different sounds that result from the three implementations. Let’s look closer at the three types.

Harmonic Tremolo

The Harmonic Trem is actually not a pure tremolo effect. It is really a dual-band filtering effect that alternately emphasizes low and high frequencies. The end-result is a soothing pulse that has shades of a mild phaser effect combined with tremolo due to the nature of the frequency bands that are alternated. This circuit required two tubes to create a two-phase differential LFO that controls the gain of the two frequency bands, and then another tube to sum the two bands together. This implementation had a rather short period of availability perhaps due to the somewhat ‘expensive’ implementation. The basic idea is shown below:

FIG. 2 HARMONIC TREMOLO BLOCK DIAGRAM
FIG. 2 HARMONIC TREMOLO BLOCK DIAGRAM

 

One phase of the LFO signal is added directly with the low-band input signal, while the other phase gets added directly to the high-band signal. Essentially, the filtered signal ‘rides’ on top of the LFO signal on its way into the tube summing amplifier. This effectively changes the small-signal operating point of the filtered signal along the tube gain curve. When the LFO signal is at low voltages, the filtered signal will have more gain as the tube operates in its steepest gain region. Conversely, when the LFO is at higher voltages, the tube gain-curve flattens out, and the input signal experiences reduced gain. Since the two bands have opposite phase LFO signals, when one band is experiencing high gain, the other is experiencing low gain. When the two are combined, the opposite phase LFO signals cancel each other out, and the two alternating amplitude-modulated filtered signals comprise the output. This produces the tremolo effect of hearing a loud (bright) signal alternating with a soft (dark) signal.

Also, as a consequence of riding up and down the tube’s gain curve, the filtered signals experience slight changes in harmonic content due to the changing nonlinearities of the gain curve around the signal. This adds further complexity to the trem’s sound.

Power Tube Tremolo

Next in line was a more cost effective circuit that eliminated two tubes from the Harmonic Trem implementation. It used the LFO signal (no longer a two-phase LFO) to directly influence the power tube bias of the push-pull output stage.

FIG. 3 POWER TUBE TREMOLO BLOCK DIAGRAM
FIG. 3 POWER TUBE TREMOLO BLOCK DIAGRAM

 

In a push-pull power amplifier, two tubes are employed and biased so that they idle at substantially less than full power. This keeps power dissipation to a minimum when no signal is going through the amp, allowing them to provide power to the speaker more efficiently while increasing tube life. The guitar signal is split into opposite phases so that one tube conducts when the signal is positive, and the other tube conducts when the signal is negative. The two outputs are added together through the output transformer.

By applying the LFO to the bias, the power tubes are being biased into lower and higher idle currents. At low idle currents, the tubes are shutting off and signal gain (volume) is reduced. At higher currents, the tubes are running hot and higher gain results. This alternating gain produces the tremolo effect.

But there is more going on than just a change in volume. Secondary effects coming into play are crossover distortion as the tremolo volume heads towards zero and the tubes are shutting off. At the other end, increased power tube harmonic distortion occurs as the tremolo nears its maximum volume. The effects of power-supply sag also contributes to some of the dynamic response when playing through this kind of tremolo circuit, as it influences the relative bias point of the power tubes. All these things add up to contribute to the ‘magic’ of this trem circuit.

Photocell Tremolo

The Photocell tremolo uses a light-dependent resistor (LDR) to attenuate the input signal. The LDR is coupled with a miniature light bulb that is connected to the LFO. As the LFO oscillates, the bulb gets brighter and dimmer which in turn varies the resistance of the LDR. The varying resistance works with other circuit impedances to change the signal level.

FIG. 4 PHOTOCELL TREMOLO BLOCK DIAGRAM
FIG. 4 PHOTOCELL TREMOLO BLOCK DIAGRAM

 

The light element used in the classic photo-trem circuits in the 60s was a neon bulb which has a very fast response time, meaning it turns on and off very quickly and spends very little time in between. This produces a characteristic ‘hard’ sounding tremolo that is moving between two levels, almost like a square wave. The duty cycle (symmetry) of the tremolo depends on the characteristics of the bulb relative to the LFO voltages, but the classic Photo-trem circuits were tuned to spend most of their time at the higher output level (duty cycle >>50%, bulb is ‘off’), switching to the lower level only briefly during the cycle. At maximum intensity, a choppy trem results.

Also, as the photocell trem circuit is not buffered, the tremolo creates a varying load resistance in the signal path as the bulb changes the resistance of the LDR. This in turn has secondary effects on the signal’s frequency response that contribute subtle characteristics as well.

Capturing the Magic

We can see from the discussions above that the end result of these vintage tremolo circuits is much more than a simple cyclical volume fluctuation. The depth, warmth and overall vibe of each one of these tremolo types can only be created by giving consideration to the entire circuitry used in the process. For the harmonic tremolo, the interaction of the LFO with the input signal in relation to the preamp tube’s operating characteristics must be accounted for. The Power-tube tremolo must recreate the vintage push-pull power tube section including the phase-splitter, tube characteristics, and power supply considerations. The photocell trem must involve the proper bulb-LDR characteristics in relation to the LFO signal, along with secondary consideration of variable loading in the signal path. When these things are all properly accounted for, the difference from a simple VCA tremolo is apparent. The complex and subtle nuances come to life, producing the mojo of their vintage amp brethren.




Flint Reverb Summary Paper – Three Classic Reverb Types

Posted by Ethan

Flint Tremolo & ReverbThe magical combination of tremolo and reverb is the earliest example of a perfect guitar effects marriage. Our new Flint Tremolo & Reverb pedal delivers three classic tremolo circuits, along with three completely unique and complimentary reverb types.

You get the classic ’60s Spring Tank Reverb, the inventive ’70s Electronic Plate Reverb, and the nostalgic ’80s Hall Rack Reverb. Pete Celi, our Lead DSP Engineer and Sound Designer illustrates the research and sound design process that went into creating our reverbs in Flint.

 

Flint Reverb Summary Paper – Three Classic Reverb Types

The ’60s Combo Amp Spring Tank

The full-size 2-spring tank was commonly used in vintage amps, and it continues its popularity today for its classic tones. The 2-spring tank uses spring segments of differing delay times (a function of the mass and tension of the spring), which adds to the complexity of the sound and smooths out the time and frequency response of the reverb. Contributing greatly to the sound are the input (driving) and output (recovery) tube circuits. These circuits are designed to reduce low-end boominess and to minimize coupling of the low- frequency cabinet resonance into the tank. The high frequencies roll off naturally due to the limits of the spring’s ability to transmit the shorter wavelengths of the higher frequencies.

FIG. 1 SPRING TANK REVERB
FIG. 1 SPRING TANK REVERB

 

The signal from the driving circuit drives a coil which in turn produces a fluctuating magnetic field that moves a magnet attached to the spring. This results in a twisting wave that travels down the spring. The time it takes for the wave to travel down the spring is a function of frequency, with lower frequency waves traveling down the spring more quickly than higher frequencies. This accounts for the ‘drippy’ or ‘boingy’ sound that the reverb produces when given a percussive attack. At the other end of the spring, the signal is recovered by the inverse process which includes coils, magnets, and a recovery circuit. In addition to being recovered, the wave will continue to reflect back and forth along the spring, creating a wash of reverberation that evolves in time due to the frequency-dependent delay times of the spring. The length of time that the reverb lasts when given an impulsive input is known as the ‘decay time’, which is controlled by physical dampers that absorb energy from the spring.

At low mix levels, the 2-spring tank adds a depth and dimension to the sound. Generally speaking, the 2-spring combo-amp reverbs tend to sound a bit less splashy and trashy than their 3-spring stand-alone counterparts at the extremes, but add a full, integrated explosion of sound when cranked up.

The ’70s Electronic Reverb

During the 1970s, digital electronic systems advanced to the point where high-quality real-time electronic reverberation was possible. A single memory chip was capable of storing 1024 bits, and the possibilities seemed endless. The most famous early electronic reverb was a $20,000 plate-style reverb that used eighty(!) of these memory chips. The amazing hardware-based algorithm used multiple delay- lines configured in parallel, with each delay featuring multiple output taps and filtered feedback paths.

FIG. 2 SIMPLIFIED ELECTRONIC PLATE REVERB STRUCTURE
FIG. 2 SIMPLIFIED ELECTRONIC PLATE REVERB STRUCTURE

 

The lengths of the delay lines and individual taps were derived mathematically to produce the most natural reverberation. The reverb algorithm also employed modulation by mixing various taps under internal control to create changes in reflection phases to further reduce undesirable resonances and add depth. The result is a rich, smooth reverb with a quick build-up in density due to the summation of the many parallel output taps.

The ’80s Hall Studio Rack Reverb

By the late ’80s, continued advances in digital ICs and microprocessors lead to (relatively) low-cost digital reverbs that could run many different reverb algorithms and allowed for preset storage and deep parameter editing. Cost sensitivity and the limited available processing power of the day led to the necessary invention of efficient algorithms with minimized computational and memory requirements. To create a Hall-style reverb, a well-practiced technique was to create an early reflections section that fed into a late reverb generator.

FIG. 2 SIMPLIFIED '80s HALL REVERB
FIG. 3 SIMPLIFIED ’80s HALL REVERB

 

A simple multi-tapped delay line was sufficient to create early reflections. The late reverberation was accomplished by a regenerating ‘series-loop’ of delays, all-pass filters, and low-pass filters. Inputs could be injected into the loop in more than one place, and the outputs might consist of the summation of several points from the loop. Delay-line modulation was employed to reduce artifacts and achieve a smoother, more pleasing decay. These hall reverbs have a signature sound of distinctive early reflections followed by the slowly-building density of the late reverberation. The modulation adds an increased sense of warmth and depth.

Enter the World of Flint

The three reverb types in Flint pay homage to these three classic reverb sounds. While not focusing on any specific recreation, these classics served as philosophical and sonic guides in the creation of our ’60s, ’70s and ’80s reverb types.




Maxwell’s Silver Hammer of the Gods

Posted by Ethan

Gregg StockOur very own Analog Guru and co-founder Gregg Stock recently had the opportunity to contribute an article for the March 2012 issue of Premier Guitar magazine.

In 1830, Michael Faraday submitted his most famous piece of scientific legislation‚ and this bit of genius described the physics that allows guitar pickups to exist. In this article, Gregg goes over the inner workings of guitar pickups, and how pickup loading can affect your true bypass pedals.

Read the article




We’re working on something new….

Posted by Ethan

Hey there! We’re hard at work on something new called Flint. We’re not quite ready to release it yet. To be notified when we do, please sign up for our email newsletter. Thanks! :)






 
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