Filters and effects ( 95 ) :

• Equalizers and filters

• 3 KHz low pass filter plus audio amplifier - circuit uses a switched capacitor filter IC MF6-50 from National Semiconductor to filter signals with frequencies higher than the 3KHz needed for voice audio, pdf file   
• Adjustable 60Hz Filter - to filter out any HUM that may be picked up by a noisy power supply or long wire connection   
• "A" Weighting Filter For Audio Measurements - design based on an old Ampex circuit   
• Basic Active Filter Circuit Blocks   
• Closing the loop deepens notches - Notch filters remove a single unwanted frequency from an input signal. They are also a vital component of pulse-shaping networks, such as time-averaging filters.   
• Design of Passive Crossovers   
• Five Band Mono Graphic Equaliser - basic mono unit originally designed for improving the apparent sound quality when dubbing video   
• A Basic Introduction to Filters - application note on active, passive and switched capacitor filters, document in PDF format   
• Active Filters - Butterworth, Bessel and Linkwitz filter example circuits and equations   
• Audio Graphic Equaliser - simple 7 band equalizer   
• Basic gyrator design - basic building block of graphic EQ   
• Designing A Pocket Equalizer For Headphone Listening   
• Filters - examples of very many different filter types, good page for filter design information   
• Have Ya Ever Been Too High?? - filter that is intended to take the harshness off some sources of sound that have an upward response tilt, go to the end of page to find this circuit  
• LMC835 - Digital Controlled Graphic Equalizer IC, take also look at   
• Multiple Feedback Bandpass Filter   
• Musical Instrument (Expandable) Graphic Equaliser - standard equalizer plus bonus distortion unit   
• Notch Filter   
• Parametric And Sub-Woofer Equaliser - simple parametric equalizer circuit   
• Passive filters fill the bill at audio frequencies - Low-frequency filters, particularly at audio frequencies, usually take the form of active filters. These filters eliminate expensive inductors with windings of many turns. However, passive filters remain a viable option when you quickly need low-cost prototypes and test pieces.   
• Simple, Easy Parametric and Graphic EQ's, Plus Peaks and Notches   
• Subwoofer Equaliser Using The Linkwitz Transform Circuit - The Linkwitz transform circuit is a hugely flexible way to equalise the bottom end of a sealed loudspeaker enclosure. A speaker that is corrected using this method is flat from below resonance to the upper limit of the selected driver. The low frequency rolloff point is determined by the parameters of the transform circuit. Should the enclosure size be too small and cause a lump in the response before rolloff, this is also corrected. A conventional active crossover network is then used to divide the subwoofer signal from the main channel signals. Note that there is also a separate   
• Tone Control Circuit - classic Baxendall tone control circuit   
• Tone Control - based on TDA1524A tone control IC   
• Tone controls with 2x NE 5532 - check also   
• Active Subwoofer Filter - Here you find an active subwoofer filter with any concievable function, and in very high quality as well. This circuit is a good an inspiration for your DIY project. The function blocks can be bypassed and left out as you find adequate. This circuit has gain control, Q-boost, 15-60 Hz subsonic filter, 4th order lowpass filter, stepless variable phase control and auto-power system.   

• Crossovers

• 24db/octave Linkwitz-Riley   
• High-Performance Audio Applications of The LM833 - RIAA phono preamplifier stages and active crossover networks   
• Passive filters fill the bill at audio frequencies - Low-frequency filters, particularly at audio frequencies, usually take the form of active filters. These filters eliminate expensive inductors with windings of many turns. However, passive filters remain a viable option when you quickly need low-cost prototypes and test pieces.   
• Passive Line-Level Crossover - A passive line-level crossover (PLLXO) is a very good solution if you don't need circuits that are too complex circuits and can live with the insertion loss.   
• Renkus-Heinz Schematics - includes some crossover and speaker controller schematics   
• Schematics Of Various Tubed Crossovers   
• Subwoofer-jakosuodin(Subwoofer Crossover) - This filter is 24 dB/octave with frequency settings of 40, 50, 60, 70, 80, 90 Hz. This circuit is only the subwoofer low pass filter part. The description text of this circuit is in Finnish.   

• Compressor/limiter

• A Two Channel Noise Gate   
• Audio Amp Output Power Limiter   
• Audio compressor - A circuit for a single-channel audio compressor using a JFET to control the gain of a vitual earth amplifier.   
• Audio Limiting Circuits - This is a limiter circuit based on Silonex linear optocoupler.   
• Audio level control device - compressor circuit based on LED and photodiode   
• Compressor applications for resistive optocouplers - This application note describes compressor circuit which uses Silonex optocouplers as the audio level controlling element.
• Compressor using photoresistor - very basic circuit based on LED, LDR and OPAMP   
• Designing A Limiter For Headphone Amplifiers - review of diode-based limiter design,   
• Dynamic Range Processor - this stereo unit allows the dynamic range of a signal to be increased (expansion) or decreased (compression) by a variable amount up to 3:1, based on the SSM2120 dynamic range processor IC   
• Dynamiikan laajennin/kavennin - This is an audio signal dynamics expander/compression circuit. The circuit is based on NE571 IC. The description of the circuit is in Finnish.   
• Fast Audio Peak Limiter   
• Q&D Compressor 2 - based on SSM2166   
• Stereo Broadcast Limiter Circuit for Ramsey FM10A and FM25A transmitters   
• Stereo Compressor - Designed to lower the audio blasting that goes with TV-commercials, the unit also serves as a studio sound manipulator!   
• Teletronix LA-2A Leveling Amplifier - a vacuum tube-type leveling amplifier (more commonly known today as a compressor) for professional audio recording and broadcasting use originally made during the mid to late 1960s   
• The Morgan Compressor/Limiter   
• Ultra Simple Bass Guitar Compressor - based on LDR connected to signal cable and lamp connected to speaker output   
• "What Compressor" Page - The What Compressor is a super transparent vocal and instrument compressor that you can build.   

• Guitar effect boxes

• A Discrete FET Guitar Preamp - Runs off a 9v battery. Very high (3.0 Mohm) input impedance. Medium (6.0 Kohm) output impedance. 3 dB gain. Graceful overload. Overload happens; the circuit should clip gracefully and recover gracefully.   
• A D.I.Y. Guitar Effects Prototyping Board - A versatile DIY Guitar Effects Prototyping Board. The best way to experiment is by using a "breadboard". A breadboard is simply just some molded plastic with a series of openings 1/10" apart, connected in rows by metal clips on the underside of the breadboard. Since guitar effects circuits all have some things in common, such as input and output jacks, volume and/or gain controls, tone controls, etc., you can permanently mount the breadboard, some spare pots and jacks to a piece of wood and hard wire them to the breadboard. Also links to guitar stompbox circuits, guitar amps and other useful information related to electric guitar.   
• Analog Music Zone Guitar Effects Schematics - guitar effects, compressors   
• A Phase Shifter Effects Box - The object of this experiment is to design a phase shifter circuit for special effects audio signal processing.   
• Aron's Stompbok Page - Want to build your own Guitar Stompboxes? It's not that hard. It takes time and patience , lots of reading, and a few skills.   
• Digital Echo Unit - mono unit for producing special effects for amateur dramatics   
• Distortion Effect (for guitars) - three distortion circuit ideas   
• Effect Rack Unit - contains very many guitar effect unit circuit diagrams   
• Effectronics Schematics - audio processing and effect circuits   
• FET Preamp Cable - Preamp Cable is a phantom powered discrete FET (Field Effect Transistor) preamp built into the plug of a guitar cable. It provides almost all the advantages of an on-board preamp.   
• Guitar Amplifiers - Guitar amplification is a specialised field, where much commonly understood theory does not apply, and little theory is published. Technically speaking, a guitar amplifier has a specific type of non-linear gain at its signal extremes, and a specialised type of limited frequency response. This article collection has lots of information on guitar amplifiers.   
• Guitar Amplifier Basics - This document tells about the technology of guitar amplifiers.   
• Guitar Amplifiers Overdrive & Distortion Effect Circuits   
• Guitar Effects Boxes - guitar effect schematics and articles   
• Guitar Effec Circuits - Wah, Fuzz and sustain circuits   
• Guitar Fuzz Effect - very compact circuit    Rate this link
• Guitar Reverb Pedal - circuit for a guitar spring reverb pedal, it has dry, wet, and drive controls for a wide variety of sounds   
• Guitar-related Circuits - effect circuit collection   
• Guitar Vibrato Unit   
• Harmony Central - contains effect information,   
• Humbucking & Noise-Reducing Electronics for guitars   
• Musical Instrument (Expandable) Graphic Equaliser - standard equalizer plus bonus distortion unit   
• Not Just Another Headphone Amp - This is a simple battery-powered musician's practice and monitoring amplifier for guitarists.   
• Skills, Tips and Tricks; How To Build Guitar Effects   
• Slew Rate Control - A circuit that limits the rate of change of a signal; a feature of this design is that the positive and negative rates can be different.   
• Spring Reverb Unit For Guitar   
• Stage Center Reverb Unit - simple spring reverb unit   
• The GEO-Fex collection of vintage and new-design effects and musical related DIY   
• The Guitar Effects Oriented Web Page - FAQs and circuit diagrams   
• The Guitar Effects Oriented Web Page - Home of the Guitar Effects FAQ, the Tube Amp FAQ, the Tube Amp Debugging Page, and "The Technology of" effects series.   
• The Technology of the Tube Screamer - The Tube Screamer series of distortion/overdrive boxes from Ibanez has a reputation that has led them to pass into musical urban myth. Helped along with Stevie Ray's use of them, the TS 808 and TS 9 have been sought after and traded up to astronomical prices. All the members of the TS family share a common technical design, with the similarities vastly overwhelming the differences. This document describes the technologies used in them.   
• The Technology of Wah Pedals - The stock "wah" pedal has been around since at least the early 60's. This thing produces a distinctive tone that is well loved by the expressive guitarist. What a wah does is clear - it is either a bandpass filter or an overcoupled lowpass filter that exhibits a resonant peak just at its lowpass rolloff frequency. The resonant peak can be moved up and down in frequency by the player, and this makes for a striking emulation of the human voice making a "waaaah" tone, or its tonal inverse, "aaaooow".   
• Vox AC30 Guitar Amplifier Simulator   

• Vocal elimination

• CD Buddy - Karioke device   
• The Truth About Vocal Eliminators - sometimes a vocal can be removed almost completely, but just as often the results are disappointing, just information without circuit diagrams   

• Noise limiter / noise gate

• Philips' Dynamic Noise Limiter - This four transistor circuit is claimed to be developed by Philips to improve the subjective signal-to-noise ratio of cassette reproduction. It works on playback only and therefore can be used with any source material. Indeed, it can improve the sound of not only tape playback but any source where broadband noise (hiss) is troublesome - noisy radio signals are examples.   

• Misc effects

• Build A Stereo Synthesizer - different frequency ranges appear at the two outputs, depending on the setting of the controls and create a stereo effect   
• Burwen audio processor documentation - dynamic noise filter and eliminator circuit diagrams   
• Digitally Control Phase Shift - Altering the phase response of a signal without changing its amplitude characteristics is commonly performed using an allpass filter. This circuit implementation is well suited to using digital potentiometers as the controlling element.   
• Dimension Control - This circuit controls the "wideness" of the stereo signal.   
• Mixed feedback drive circuits for audio output transformers - technical paper from   
• Square wave to sine wave converter circuit   
• Stereo Width Controllers - vary the width of the "sound stage" when listening to stereo recordings   
• Synthfool - many musical instrument and effect circuit diagrams   

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