Audio Modulation Components

 

developed By

 

Adam S. Arterbery

&

Vijal Parikh

 

12/6/2005

 

Electronics For Neurobiology (Bionb 440)

Deapertment of Neurobiology and Behavior

Cornell University

Ithaca, NY

14850

Introduction:

 

        In the music industry today technology sets the pace for new trends in creative capacity. At the center of all studio recording and live performance in the music industry is the continuing technological advancements of audio-modulation. This webpage explains the development of four audio-modulation components intended for use in studio and live performance capacities. The components range from classic re-rendered effects to more modern depth effects using harmonics and tone bending. The focus of the integration of these components as a functional part of the music industry is intended to provide new creative capacity for musicians and technicians as well as provide a fundamental integrated modulation to be used for an instrument or audio input.

The following includes circuit pictures, circuit schematics, and explanations for each of four audio modulation components developed: 1) A three band equalizer with frequency ranges for high, mid, and low modulation. 2) A fuzz generator which turns any input into a grunted-crunch output. 3) A harmonic sweetener which clips higher frequencies and adds them on top of the straight feed at the output. 4) A tone bending circuit which enables the tone quality of any input to bent toward either extreme (high/sharp, low/flat). Finally, future modifications and applications are discussed as well as problems that must be resolved.

 

 

 

*Note: All circuits are intended for use with 9-12 volt power supply.

 

 

Three Band Equalizer:

 

This circuit boosts or cuts off +/- 20db at three frequencies of 50Hz (low), 1 kHz (mid) and 10 kHz (high). The supply voltage maybe anything from 6 to 30 volts, with maximum boost of 20db occurring with maximum supply voltage. For our purposes in this circuit design, 9 volts was used as the supply voltage, so maximum boost is considerably less than 20db. Three 100k trim potentiometers are used to control the low, mid and high boost/cutoff. The top segment of the circuit is the low pass element, the middle element is the band pass and the lower segment of the circuit is the high pass element.

 

 

                            

All elements connect to one op amp (LM358), with the output of the op amp containing the modified sound with equalization. Operation of the circuit includes changing the various trim pots to allow boost of cut off the three frequencies. When the trim pot is in its center position, no boost or cutoff is seen. When the trim pot is to its left most position, the greatest amount of cutoff of whatever frequency that trim pot is regulating is seen. Lastly, when the trim pot is to its right most position, the greatest amount of boost occurs.

 

Three Band Equalizer Circuit Picture:

 

 

Three Band Equalizer Circuit Schematic:

 

 

Fuzz Generator:

 

        The fuzz generator is a classic effect used with guitars, and this circuit is based on the original fuzz circuits. This application is intended for use with all audio input to generate a grunted-crunch (at low frequencies sounds similar to the old motorcycle sounds from the original Nintendo). The circuit is really basic but sounds very good. It is recommended that it be used at max or close to max capacity of the potentiometer (three red wires at bottom left in picture) to produce a prominent and sufficient fuzz tone.

 

Fuzz Generator Circuit Picture:

 

 

 

Fuzz Generator Circuit Schematic:

 

 

 

The schematic shows the circuit connected to an oscilloscope and using one operational amplifier (LM358). The switches at the input and output allow for an effective bypass for the straight line input through the circuit.A fuzz circuit generates a deliberately distorted version of the input signal. A traditional fuzz circuit boosts and clips the signal sufficiently to turn a standard sine wave input in to what is effectively a square wave output. This gives a much more distorted and synthetic sound than a standard distortion or overdrive. Due to cross-modulation of signal components fuzz effects are usually used along with power chords to reduce dissonance.

 

 

Harmonic Sweetener:

 

        The input of this circuit is amplified by the first op amp, in which the output goes to two different elements in this circuit. The bottom half of the circuit is the clipper segment. The amplified signal goes through four other op amps, in which the wet signal that comes out of the 4th op amp in the clipper segment is clipped. This clipped signal is then outputted to a 10k trim potentiometer which controls the amount of clipped signal is added to the original amplified signal. The last op amp is an adder in which the original amplified signal and the wet clipped signal is added up and sent to the output. A drawing of what happens when the signal goes through the various circuit elements is provided below:

 

                       

 

 

Harmonic Sweetener Circuit Picture:

 

 

 

 

Harmonic Sweetener Circuit Schematic:

 

 

Tone Bender:

 

        The tone bender is a circuit meant to add a touch of sway to a whole tone. The bend refers to the fact that the circuit bends the natural frequencies in an input tone toward a sharpened edgier tone or a duller, more flat tone. This dynamic tone control is useful for creating sustain effects and overtone feedback effects. The idea is to have one potentiometer controlling master mix coming out at the output and have another potentiometer to control the range of frequencies that the circuit bends. However, making the frequency range fully audible to the human ear requires this potentiometer to at least be an audio taper. The 8.2 K resistor running to ground from this pot was replaced with a 1 M resistor. In addition the range of the dynamic frequencies needs to be considered and perhaps broadened. The circuit uses two transitors and two potentiometers. It runs off a 9 volt supply and provides strong modulated tone-quality.

 

Tone Bender Circuit Picture:

 

 

Tone Bender Circuit Schematic:

 

 

Future Modifications and Applications:

 

        Future work includes adding a bypass system such that when a switch is pressed, the effect is applied to the dry signal. When the switch is pressed again, then the effect will not be mixed with the dry signal and the input will be routed to the output. This can be done manually by switching where the input goes to (i.e. the input could go to the effect or the input can go directly to the output). However by using relay switches and LED indicators to tell the status of the switch, switching between various effects will occur faster and will be more efficient. Two different switching circuits that could be implemented are shown below:

 

 

Modifications to these bypass circuits are underway to implement to the effects.

 

        Covering the effects with enclosures is also another modification that will be implemented to preserve the effects and prevent them for damage. Various enclosures can be purchased with electronic companies such as digikey.