The Phaser E-stim Reference and Glossary
| | E-stim
E-stim, or estim, stands for electrostimulation
and means a technique to pass an electric current from one electrode, through living tissue, to another electrode. Sensory perception depends on various variables such as the size and placement of the electrodes, the applied pulse waveform
of the stimulating current, and the pulse repetition frequency.
E-stim is usually broken down into different categories such as electromedicine, electrotorture, electrosex, and electropleasure, the latter meaning pleasure through the erotic use of electricity.
Besides the electrodes, e-stim requires an electric stimulation power source, a device that delivers a pulsed current to the electrodes. For electromedical applications TENS units are widely spread, and quite often, the same TENS units are repacked and sold as electropleasure devices.
But more and more the market for e-stim units gets dominated by devices specifically designed and manufactured for erotic use. Prices vary from $60 for a simple TENS machine to $600 for a more sophisticated multichannel e-stim device
Another approach is to use an electric stimulation software
such as Phaser, an amplifier and a step-up transformer circuit, also referred to as a Phaser Circuit
, to generate the stimulating pulses in a most flexible way, creating stimulation effects that are not achievable with off-the-shelf equipment.
A growing electrostimulation DIY community prefers homemade devices, also known as White Boxes
Electrostimulation with a Phaser Step-up Circuit
An e-stim device is a self-contained box that is specifically designed for electrostimulation. Most units are battery powered, some have built-in rechargeable batteries, and some devices come with a mains adaptor that boosts the maximum available output power if plugged in during operation.
The first electric stimulation device to be sold in large quantities is said to be the RelaxAcizor.
Microprocessor controlled E-stim Device
The latest generation of e-stim units are digital devices, controlled by a microprocessor inside the box. A designer software running on a PC allows to upload new routines into the device.
More enhanced devices even process audio signals and audio files
that are fed to the unit via an audio input jack. Our electrostimulation software
Phaser is suitable for driving e-stim units via the audio input, introducing new sensations and allowing secure and encrypted remote control over the Internet.
| | DIY E-stim White Box
A White Box
, in the context of electric stimulation, denotes a homebrew DIY e-stim box that connects to a computer's sound card or to another interface. It usually consists of electronic parts which form a Phaser Circuit
, and optionally a power amplifier.
There are various reasons why people start building their own electrostimulation equipment. The first thing that comes to one's mind is, of course, saving money. Good e-stim equipment does have its price, but apparently not everyone is willing to pay such price. Another motivation is the ability to produce levels and sensations that are not achievable with off-the-shelf e-stim devices.
The photo shows a DIY Phaser Circuit that makes use of 6 transformers. The box connects to a power amp driven by audio signals from a computer.
Homebrew 6 Channel DIY E-stim White Box
| | E-stim Software
E-stim software usually means a desktop or laptop computer application that generates audio signals intended for e-stim, and outputs these signals in real-time through the computer's sound card.
These e-stim audio signals are either fed through an amplifier to a Phaser Circuit
, or they directly drive an e-stim device
. They can also be written to disk as e-stim sound files
for use with other units.
Recent software allows to choose between different pulse waveforms
and to modulate the signals. You may also find level displays, waveform viewers, features to measure frequency and pulse response of step-up circuits, and dynamic pulse enhancers.
Electrostimulation software usually comes with a set of ready-to-run sessions that can be tailored to your needs and saved as shareable files.
The safe and encrypted PRP
protocol of Phaser even allows e-stim remote control and chat.
While most e-stim software targets Windows only, Phaser is a true multi-platform solution, providing a distinctive platform-independent appearance with a standard behavior, running on Windows, Mac OS X, and on most common Linux distributions.
Good stimulation software is high DPI-aware and appropriately scales to your current Desktop DPI setting without any blurring. You may also choose another scaling factor to meet your personal needs. Scaling is required for the use with high-PPI displays, which are becoming increasingly popular on tablets and notebooks.
On the right you see 3 instances of Phaser running simultaneously on OS X, at different scaling factors.
3 x Phaser on Mac OS X @ 100 %, 150 %, and 200 %
| | E-stim Waveforms
It is commonly accepted that the most effective e-stim waveform is a low duty cycle pulse
train. In contrast, sinusoidal signals require a linear power amplifier and a low distortion step-up
transformer circuit. The average energy delivered to the tissue by sine waves is much higher than with optimized LDC pulses. However, sine waves are particularly suitable for exploiting interference effects like the Phaser Effect
, and thus are commonly used with StereoStim devices.
The Phaser bPulse
waveform is a bi-directional, balanced LDC pulse that has its interphase interval maximized. This delay between the charging and discharging pulse lowers the excitation threshold, and thus also lowers the total energy delivered to the tissue. This is our preferred pulse shape for electrostimulation.
The Phaser iPulse
waveform makes use of a fixed interphase interval, which is equal to the pulse width of the signal. This is the recommended e-stim waveform for repetition frequencies below 80 Hz.
Both the bPulse
and the iPulse
pulses are DC compensated, i.e. they do not have a DC offset, which is also true for the Sine
Bi-directional pulses, also referred to as biphasic or bipolar pulses, have less average power than sine waves. The average power depends on the pulse width and the pulse repetition rate of the electric stimulation signals.
Energy-efficient waveforms for use with e-stim are the two optimized LDC pulses that our Phaser software emits.
Low Duty Cycle pulse waveforms reduce the tissue power dissipation at the skin-electrode interface, compared to a sinusoidal stimulation that induces the same sensory perception.
Minimizing the delivered energy is of particular importance so as to reduce or eliminate side effects like tingling, numbness or skin irritation.
Phaser's unique LDC e-stim waveform optimizes the ratio of stimulus perception to delivered energy through an interphase interval (short delay) between the charging and the discharging pulse.
Optimized LDC Pulse with Interphase Interval
| | Optimal E-stim Waveform
The first step on the road to the perfect pulse is to choose an electrode-skin model that most closely reflects the electrostimulation specific environment, and to calculate the actual values of the model's circuit elements from measurements in the lab.
After doing the math it becomes obvious that the optimal waveform (LDC
) reduces the tissue power dissipation by more than 90 %, compared to a sinusoidal stimulation inducing the same sensory perception. (Article is accessible
The pulse width should be chosen to be within the optimum operating range. Phaser's bi-phasic pulse with interphase interval is our implementation of the optimal e-stim pulse waveform.
Optimal Pulse Waveform: Power vs. Pulse Width
| | Phaser Effect
The Phaser Effect is achieved by generating sine waves with slightly different frequencies for the two channels in a Three-Electrode Setup
. This is equal to a continuous and periodic change of the phase relationship between the two e-stim signals. Thus, the combined signal amplitude varies in time with the beat frequency, which is the difference between the two interfering signal frequencies.
Fig. 1 shows two sine waves L and R. R does have a slightly higher frequency than L, thus increasing the phase difference with time. The green line is the combined signal L + R, the electric stimulation current through the corona electrode if using this Phaser Circuit
, slowly varying its amplitude with the differential beat frequency.
Using LDC pulses
presents a new problem when it comes to exploiting the interference beats for e-stim purposes. In Fig. 2 two biphasic pulse trains with slightly different frequencies are shown, the blue pulse train having a slightly higher repetition rate. The thing with low energy pulses is that there is nothing, most of the time. That's why it's low energy. Combining both signals does not result in a nicely modulated signal, but in a more or less randomly looking pulse train with some rare peaks when the pulses L and R overlap (green peaks).
The solution here is to apply AM modulation in combination with 180° phase shifts to one of the emitted pulse trains.
In Fig. 3 modulation and phase switching is applied to the pulse train R (blue), the black arrows marking the points of the 180° phase switches. The result is quite comparable to that of sinusoidal interference beats, but at a greatly reduced energy level.
Fig. 1 Phaser Effect: Interference Beats
Fig. 2 LDC Pulses and Interference Beats
Fig. 3 Phaser Effect with LDC Pulses
A Phaser Circuit, also Phaser Step-up Transformer Circuit, essentially is a combination of UL listed low cost mains transformers and a resistor network.
The circuit acts as a high impedance current source in order to maintain a constant stimulation current independent of the load impedance.
The output impedance should be at least ten times the load impedance to achieve current source characteristics, i.e., 10 kΩ or higher, way better than the typical 500 Ω of most off-the-shelf e-stim devices and TENS units.
Encapsulated and vacuum potted low cost mains transformers are usually used to convert the AC mains voltage to a rather lower voltage. Using them in reverse and outside the frequency range they are optimized for requires some extra research, as frequency response plots for the entire audio range are usually not available from the manufacturers.
So we tested different samples from various makers for their usability in a Phaser step-up circuit.
Phaser Step-up Transformer Circuit for E-stim
Most transformers are designed for both the US and European market and hence come with two primary and two secondary windings. Connecting the two primary windings in series and the dual secondary windings in parallel gives the best turns ratio.
Our step-up circuit dissipates more than 90 % of the supplied input power as heat in the resistors, the price to pay for a passive current source. And exactly this high power dissipation is the reason why battery-powered, lightweight e-stim boxes have a relatively low output impedance (300 to 500 Ω). Converting most of the power into heat would suck the battery dry pretty quick.
On the other hand, the Phaser Circuit is robust, short-circuit and open-circuit proof, and adds yet another layer of security to the setup.
Tested Transformers for the Phaser Circuit
If power consumption is not a concern, a passive high impedance source is the absolute first choice for any high quality step-up circuit.
The transformer circuit forms a low-pass filter with a roll-off of -6 dB per octave. To improve the frequency response of the step-up circuit, this roll-off must be compensated for. This can be done by applying a pre-emphasis filter function to the stimulation signals that boosts the high frequency components.DynaShape
is our implementation of such a digital filter with adjustable cutoff frequency.
The Phaser step-up circuit is the reference for the development of all our e-stim patterns.
Typical Step-up Transformer Frequency Response
| | DynaShape
The Phaser DynaShape
pulse enhancer is a digital filter that compensates for the low-pass filtering effect of step-up transformer circuits.
To preserve the original e-stim pulse waveform, the necessary step-up transformer circuit, the Phaser Circuit
, must have a flat frequency response curve. Usually these transformer circuits have a low-pass characteristic. DynaShape
applies a pre-emphasis filter function to the e-stim signals that boosts the high frequency components and thus flattens the frequency response curve, as shown on the right.
DynaShape Frequency Response Boost
| | Three-Electrode Setup
The Three-Electrode Setup, also Tri-Phase Setup
, combines two e-stim signals from two independent channels to drive three electrodes. If properly used with stimulation signals that exploit interference beats, a pleasurable Phaser Effect
It is most important to maintain the correct phase relationship of the two signals by observing the transformer polarity markings of the Phaser Circuit
Most of the e-stim sessions and templates of our software were designed for a three-electrode setup.
Three-Electrode Setup: Wiring of E-stim Electrodes
| | E-stim Audio Files
E-stim audio files are specifically crafted sound files that are played through an amplifier and a step-up transformer circuit, a Phaser Circuit
, and deliver stimulation pulses to appropriate electrodes. Some of the commercially available e-stim devices
are also equipped with an audio input jack and can process e-stim sound files fed into the audio input.
Electrostimulation audio files are either played from a digital player, a CD player, or from a computer.
E-stim audio files tend to be large and often are digitally compressed
to save disk space and hence transmission time over the Internet. Lossy compression methods like the very popular MP3 algorithm alter the digital data in an irreversible way and thus should not be applied to any e-stim audio signals.
A Low Duty Cycle (LDC) E-stim Audio File Example
E-stim sound files are available on the Internet or sold on CDs through retailers. To create or edit electrostimulation audio files, audio editor software can be used. Tools like Expression Evaluators allow sound to be generated from almost any equation. Some clever minds quickly adopted this to e-stim and published a wide variety of formulas to evaluate pleasurable stimulation sounds.
A major drawback of expression evaluation is the tedious process of generating the complete sound file over and over again for each change made to its parameters. This is where the Phaser software kicks in, generating stimulation signals in real-time.
E-stim Signals generated using math. Expressions
| | Compression of E-stim Audio Files
Compression of electrostimulation audio files
is used to reduce the file size. Lossless compression retains all data of the original sound file, while a lossy compression algorithm eliminates bits of information to reduce the size of the file.
Lossy audio compression methods like MP3 and WMA were designed for music. Depending on the selected bit rate, the signals get altered more or less. While these algorithms were optimized to remove those details that most people's ear would not pass to their brains, this can be disastrous if applied to e-stim signals.
On the right is an electrostimulation signal, and below the signal after compression / decompression with different codecs. The popular 128 kBit/s MP3 compression, good for most music downloads, adds noise and ringing, and removes most of the necessarily intended DynaShape
To understand why the test signal is altered in such a way, we have to look at the encoding scheme. Those parts of the audio signal that humans perceive distinctly are coded with high accuracy, less distinctive parts are coded less accurately. Parts of the sound, which we do not hear at all, are mostly discarded. That is removing information from the signal, hence destructive compression!
The higher the bit rate, the less information has to be removed from the signal. That's why the 320 kBit/s signal looks more like the original, at the price of file size, but there still remain some compression artifacts, ringing and noise.
Low Duty Cycle (LDC) E-stim Audio Test Signal
MP3 compression with CBR 128 kBit/s
MP3 compression with CBR 320 kBit/s
For a real world test we designed an AM and FM modulated LDC
e-stim audio wav file with different parameters for each of the stereo channels. The total length of the sound is 60 s, the uncompressed file size is 10.34 MB.
FLAC, the Free Lossless Audio Codec, although set to maximum compression, does not really do a good job. Even the old ZIP algorithm compresses about ten times better. The newer algorithms RAR and 7z squeeze out even more bytes, and, most important, the compression is lossless, i.e. the electric stimulation signal remains untouched.
E-stim audio files can be compressed sufficiently with lossless algorithms if they only consist of LDC pulse signals. The compression ratio is superior compared to the lossy, psychoacoustic based MP3 or WMA codecs.
Effective Compression of Different Algorithms