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AES Journal Forum: Comments on various posts

Published: Tue, 20 Mar 2018 20:25:20 -0400

Last Build Date: Sun, 11 Feb 2018 14:14:45 -0400

Copyright: Copyright 2018 Audio Engineering Society Inc. All rights reserved.

AES Journal Forum: Comment by Scott Dorsey on "Motion Picture Sound Recording at USAF Lookout Mountain Laboratory"

Sun, 11 Feb 2018 14:14:45 -0400

Title: Motion Picture Sound Recording at USAF Lookout Mountain Laboratory
JAES Volume 2 Issue 4 pp. 204-214; October 1954
Comment by: Scott Dorsey

Back in the fifties when there wasn't a lot of common knowledge about newly developed facilties and production techniques, a big part of the AES was for engineers to talk to one another and discuss what they were doing.  So you will find a lot of papers from this era that just describe facilities and those papers are very cool because they provide insight into facilities and production techniques of that era.

This is a review of the sound mixing and transfer facility at what was perhaps the world's largest industrial film production operation at the time, making publicity and training films for the US Military.  A lot of effort was put into industrial-grade 16mm production as well as theatrical-grade 35mm films for release, and so the facility has a lot in common with both small local TV production facilities as well as with big Hollywood dubbing stages.  Work had begun at this time into making stereo mixes for Cinemascope release and fitting the facility up for that.

Howard Tremaine was much more famous for his work as an author of such works as the Audio Cyclopedia than for his work doing film production for the Air Force, so this paper is a look at a different side of a well-known pioneer.

AES Journal Forum: Comment by Scott Dorsey on "Design of a Studio-Quality Condenser Microphone Using Electret Technology"

Tue, 30 Jan 2018 16:45:40 -0400

Title: Design of a Studio-Quality Condenser Microphone Using Electret Technology
JAES Volume 26 Issue 12 pp. 947-957; December 1978
Comment by: Scott Dorsey

Two previous versions of this paper had been given at conventions, but this one, published in the JAES, is the final and most complete one.  This is the paper that introduces the SM-81 and which contains a schematic of the early SM-81 (although people using this information for maintenance should beware that over the many decades in which the SM-81 has been manufactured the electronics have been completely revamped several times).

This paper is interesting for the insight into the design process of the SM-81 and into the various constraints on microphone performance which have not changed even today.  It is a useful source of service information for people who might be repairing the SM-81.  It is a useful source of design information for people who might be designing a new microphone.  When it came out, it was revolutionary; aside from a few Sony products of limited reliability, this was the first high performance electret microphone available to studios and sound reinforcement people, and it was the first condenser microphone of any sort that would work outside in the rain.  This paper explains why.

AES Journal Forum: Comment by Scott Dorsey on "SPICE Models for Vacuum-Tube Amplifiers"

Fri, 01 Dec 2017 11:32:22 -0400

Title: SPICE Models for Vacuum-Tube Amplifiers
JAES Volume 43 Issue 3 pp. 117-126; March 1995
Comment by: Scott Dorsey

This paper was written when computer modelling was a brand new technology and when even transistor models were comparatively crude simulations based on a few constants and the Ebers-Moll equations.  The whole notion of trying to simulate a vacuum tube system electronically was just totally off the wall.  People weren't thinking about trying to emulate the sound of tube circuits back then, they were just looking for a simple tool to help designers.

So, this is a simple first order model that merely describes triodes and pentodes as linear functions.  It doesn't include Miller capacitance.  It doesn't include any weird leakage effects.  It's based entirely on a model of function, not on a model of the internal physics.

But it exists.  It was totally off the wall, coming at a time when there was little to no serious interest in tube circuit designs, and coming from an academic who had a history of working hard to eliminate tubes by finding and solving aberrations in solid state circuits.

You'll find this paper cited by anyone who is working on simulation of tube systems because it was the first, it came out of nowhere, and it made people realize that it was possible.

AES Journal Forum: Comment by Scott Dorsey on "The RCA Victor DYNAGROOVE System"

Tue, 21 Nov 2017 12:08:13 -0400

Title: The RCA Victor DYNAGROOVE System
JAES Volume 12 Issue 2 pp. 98-114; April 1964
Comment by: Scott Dorsey

The Dynagroove system consists of a large number of different parts, all from RCA and all of which were implemented at the same time.  Olson's paper doesn't attempt to distinguish so much between them as merely to be an overall high level view of the recording chain RCA was using at the time.

Some of the things discussed in this paper, such as the use of peak-reading indicators to prevent tape overload, were incredible advances in technology.  Some of them, like the "dynamic spectral equalizer" which today we'd call multiband compression, were useful tools that has good and bad applications.  And some of them, such as the "dynamic styli correlator" which attempted to provide pre-distortion to improve tracking with spherical styly, seemed like good ideas at the time but in the end were complete disasters because they made assumptions about the playback system which didn't necessarily hold.

Still, this is a fascinating document, in part for historical reasons because it is a view into a real attempt to improve the technology of the day, and in part because it provides some basic philosophy on system design that holds years after the technologies were obsoleted.

AES Journal Forum: Comment by Gary Eickmeier on "Reflecting on Reflections"

Tue, 10 Jan 2017 13:57:33 -0400

Title: Reflecting on Reflections
JAES Volume 62 Issue 6 pp. 454-455; June 2014
Comment by: Gary Eickmeier

There might be flutter echo if you were doing it in a bare room, but not in a room designed for audio - either production or reproduction. For example, my room is 20 ft wide by 30 ft long and has some diffusers in the back half on the side walls, plus absorbent furniture at the listening position and plush throw rugs on all floors, and a cathedral ceiling. The RT60 is about 500 ms, about right for this size room. The walls near the speakers at the front of the room are flat wallboard done purposely to create a huge lattice of direct and reflected image sources. What all this means is that the first reflections are specular and occur only once, then are absorbed normally, the same as any other system. All that changes is the spatial characteristic, leaving the temporal unaffected except for what is contained in the recording. Doing the spatial by reflection like this is the only way to be able to adjust the direct to reflected ratio and make it more like the live model. It's a whole different universe with different rules. Paper to follow - hopefully!