Dynamic Motion of the Corrugated Ribbon in a Ribbon Microphone; Echoplex and SpaceEcho Models

Fri, 10/22/2010 - 3:15pm - 4:05pm
Knoll 217, CCRMA Classroom
Event Type: 
DSP Seminar
This week's DSP seminar will be another double-header, with Dan Schlessinger, a MSEE/CCRMA graduate now with Sennheiser at their Palo Alto Research Center, talking about ribbon microphone ribbon dynamics, and me giving a short overview of tape delay physical models.  The seminar will take place in the CCRMA classroom (Knoll 217) at 3:15 PM this Friday, October 22.  Abstracts follow:

Dynamic Motion of the Corrugated Ribbon in a Ribbon Microphone
Daniel Schlessinger, Jonathan Abel

Ribbon microphones are known for their warm sonics, owing in part to the unique ribbon motion induced by the sound field.  Here the motion of the corrugated ribbon element in a sound field is considered, and a physical model of the ribbon motion is presented. The model separately computes propagating torsional disturbances and coupled transverse and longitudinal disturbances.  Each propagation mode is implemented as a mass-spring model where a mass is identified with a ribbon corrugation fold. The model is parametrized using ribbon material and geometric properties.  Laser vibrometer measurements are presented, revealing stiffness in the transverse and longitudinal propagation, and showing close agreement between measured and modeled ribbon motion.

Digital Models of the Roland RE-201 SpaceEcho and Maestro Echoplex EP-4 Tape Delays
Jonathan Abel, David Berners, Steinunn Arnardottir, Kyle Spratt

Digital emulation of tape echo is considered, focusing on two popular units, the Roland Space Echo, released in 1973 and used widely in dub and reggae music, and the Maestro Echoplex, released in 1959 and popular among guitarists.  Key to the sonic character of these units is the mechanics of the tape delay transport which produce a fluctuating time delay, modeled here by quasiperiodic capstan and pinch wheel components and a noise-like drift term.  The SpaceEcho time delay is controlled by varying tape speed across fixed record and playback heads, while the Echoplex provides a moveable record head, and can generate large frequency shifts, including "sonic booms" and shifting of the tape bias signal into the audio band.  An interpolated write employing a variable anti-aliasing cutoff frequency is described for implementing the moveable record head.  

Open to the Public
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