1 Analysis and Implementation Analysis and Implementation of the Guitar Amplifier of the Guitar Amplifier Tone Stack Tone Stack David Yeh, Julius Smith David Yeh, Julius Smith dtyeh,[email protected]dtyeh,[email protected]CCRMA CCRMA Stanford University Stanford University Stanford, CA Stanford, CA
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Analysis and Implementation of the Guitar Amplifier Tone Stack
Analysis and Implementation of the Guitar Amplifier Tone Stack. David Yeh, Julius Smith dtyeh,[email protected] CCRMA Stanford University Stanford, CA. Digital audio effects that emulate analog equipment are popular. “Modeling” amplifiers - PowerPoint PPT Presentation
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Analysis and Implementation of Analysis and Implementation of the Guitar Amplifier Tone Stackthe Guitar Amplifier Tone Stack
Digital audio effects that emulate analog equipment are popular
““Modeling” amplifiersModeling” amplifiers
Products by Line 6, Yamaha, Products by Line 6, Yamaha, Roland, Korg, Universal Audio, etc.Roland, Korg, Universal Audio, etc.
CAPS open source LADSPA suiteCAPS open source LADSPA suite http://quitte.de/dsp/caps.htmlhttp://quitte.de/dsp/caps.html
Emulate behavior of classic analog Emulate behavior of classic analog gear in softwaregear in software As close to real thing as possibleAs close to real thing as possible
For portability and flexibilityFor portability and flexibility
Guitar amp tone stack is a unique component in the sound of an amplifier
Almost every guitar amplifier, solid state or tube, has a tone control circuit – referred to as a tone stackPassive RC filter to audio signalLocated either directly after preamp stage or after stages of gain and buffer
Straightforward approachFind continuous time transfer functionDiscretize by bilinear transformImplement as transposed Direct Form II (DFII)Pros: Perfect mapping of tone controls to frequency response within limitations of bilinear transformCons: Complicated formulas to compute coefficients
Commercial effects pedals commonly run at 31 kHzGuitar amplifier system is bandlimited by speaker response: 100–6000 Hz.For f_s = 20 kHz, error increases but only at high frequencies due to asymptotic limits
Table lookup implementation simplifies computation of coefficients
Tabulate 25 steps of each tone control parameter = 515 kB tableLattice filter implementation for robustness to roundoff error in coefficients and to smoothly fade between coefficients as tone controls are variedConvert from z-domain transfer function to lattice coefficients by step-down algorithm