PNW Section Zoom presentation on processing out wow and flutter by John Chester (L) and Jamie Howarth (R).
PNW Section met via Zoom Oct 18 with a presentation by Jamie Howarth and John Chester of Plangent Processes on removing speed fluctuations on analog magnetic recordings using a proprietary method. Some 49 people (36 AES members) attended the Zoom.
Jamie began by playing several recorded excerpts with varying degrees of speed problems, and the results after processing, then describing his system. Analog tape recordings are known to have speed fluctuations, some of which may be described as "wow and flutter" but sometimes severe such as when a recorder's fast-forward switch is activated during recording. The Plangent Process uses custom analog playback/digitizing machines and digital signal processing to eliminate this by utilizing the bias signal on the tape as a time base. It is not a realtime process.
AC bias is a high amplitude, high frequency signal mixed with an audio signal during recording to help magnetize the tape with audio more linearly and with less distortion. Developed in the mid-20th century, the resulting higher fidelity revolutionized magnetic recording. Contrary to common wisdom, the bias signal is recorded to tape along with the audio signal, but it may be faint and be of high enough frequency to usually be undetected and unheard.
Jamie recounted how he noticed he could hear a whistle when slow-scrubbing a tape many years ago. He sat on the idea for many more years until a prototype system could be made. The hardware and software continues to be improved. Today, archival analog recordings with terrible speed problems can be corrected. Even subtle speed fixes can make an audible difference in a classic rerelease. Wire recordings have also been processed.
John Chester continued by showing the general analog recovery hardware and doing a demonstration capture playback to digital. Special wideband electronics and a highly modified Ampex ATR-102 was used, along with analysis equipment. The residual bias signal sought can be very low amplitude and the frequency varies depending on the recording machine, sometimes being over 400kHz. Higher tape speeds help here. Once the audio tracks and bias signal are digitized, Jamie does the digital processing to correct the final tracks. If there is insufficient residual bias signal, sometimes other steady-state signals, such as digital clock leakage, can be used as the speed reference.
Lively Q&As were done throughout and many people stayed at the end for self introductions and chat.
Jamie Howarth is musician, composer and audio inventor who resides on Nantucket, MA. Veteran engineer and director at various media facilities including the Hit Factory and a 20 year run at ABC TV as an audio post-production engineer and music director.
Howarth's audio restoration company, Plangent Processes has earned 2 Best Historical Album Grammy wins for The Rolling Stones' "Charley is My Darling" and "The Live Wire - a 1949 live performance by Woody Guthrie, and a 3rd nomination for Errol Garner's "Concert By The Sea". Plangent Processes has restored numerous master tapes for Bruce Springsteen, Queen, Grateful Dead, the Neil Young Archives, Doc Watson, Tim Buckley, Pete Seeger, and the Andy Warhol estate, The Owsley Foundation, among others. A mag film version of Plangent has aided soundtrack restoration for From Here to Eternity, Close Encounters of the Third Kind, Cabaret, Camelot and West Side Story among many others.
John Chester
•Live sound engineer (Chief Sound Engineer, Fillmore East, 1969-1971)
•Analog circuit designer and equipment manufacturer (Chaos Audio, 1971-1990; Modulation Sciences, Vice President R&D, 1980-1992).
•Independent consultant for A/V, video conferencing, network and telecommunications, 1992-2002.
In 2002 John began repairing and upgrading tape machines. After refreshing his memory of magnetic recording theory, he then started on all the theory he'd never learned. John then learned how to use modern digital tools to improve the performance of vintage machines.
In 2007 he met Jamie Howarth, learned about Plangent technology, and began the design and construction of the next generation of Plangent hardware. He began doing Plangent transfers in his studio. For formats larger than 1/2", he set up Plangent equipment in a studio that had the appropriate tape machine and then supervised the transfer (e.g. Grateful Dead Europe 72 multitrack, done at Sonicraft). John is an AES Life Fellow.
