Technical articles page

These are a few of my published and not published articles that I have converted to

PDF format.

They are all copyright James A. Moorer. Feel free to use these with appropriate referencing.

And about the unpublished ones

They are unpublished because either I don't feel like publishing them, or they are not finished,

or I don't think anybody would want to publish them. They may show up in a book that I may

or may not write someday, so please respect the copyright and give credit where it is due.

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Hard-Disk Recording and Editing of Digital Audio.  Presented at the 89th AES convention, September 21-25 1990, Preprint Number 3006 (K-6)

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Whither Dither: Experience with High-Order Dithering Algorithms in the Studio.  with Julia C. Wen. Presented at the 95 AES convention, October 7-10 1993, Preprint Number 3747 (B3-AM-3)

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Breaking the Sound Barrier: Mastering at 96 kHz and Beyond. Presented at the 101st AES Convention, November 8-11 1996, Preprint Number 4357 (I-2)

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Music Recording in the Age of Multi-Channel. Presented at the 103rd AES Convention, September 26-29 1997, Preprint Number 4623 (F-5)

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Towards a Rational Basis for Multichannel Music Recording. (with Jack H. Vad) Presented at the 104th AES Convention, May 16-19 1998

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A Native Stereo Editing System for Direct-Stream Digital. (with Ayataka Nishio and Yasuhiro Ogura) Presented at the 104th AES Convention, May 16-19 1998

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48-Bit Integer Processing Beats 32-Bit Floating-Point for Professional Audio Applications. Presented at the 107th AES Convention, September 24-27 1999, Preprint Number 5038 (L-3)

Scanned Copies of Older Papers

For my older papers, I don't have machine-readable copies.

A lot of them were done on text editing and formatting engines that don't

exist any more. I am starting to scan them in so I can offer PDF copies

over the net.

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The Synthesis of Complex Audio Spectra by Means of Discrete Summation Formulas Journal of the Audio Engineering Society, Volume 24, Number 9, November 1976, pp717-727. "A new family of economical and versatile synthesis techniques has been discovered, which provide a means of controlling the spectra of audio signals, that has capabilities and control similar to those of Chowning's frequency modulation technique. The advantages of the current methods over frequency modulation synthesis are that the signal can be exactly limited to a specified number of partials, and that 'one-sided' spectra can be conveniently synthesized." That was the abstract of the paper.

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Linear-Phase Bandsplitting: Theory and Applications (with Mark Berger) Presented at the 76th Convention of the Audio Engineering Society, October 8-11, 1984, New York, Preprint 2132 (session A-1) "There are a number of applications for banks of bandpass filters in professional audio studios, both for film and music production. In this paper, we explore digital techniques for bandsplitting that have the property that the spectrum may be separated into a number of bands such that when these bands are added back together, the result is a pure delay. There need be no amplitude or phase distortion other than delay. This allows such applications as linear-phase graphic equalizers, multi-band noise gates, and many other improvements over conventional studio equipment. These algorithms have been implemented on a large-scale audio signal processor and run in real time. They are currently being used in major motion picture production."

This is probably my most-misunderstood paper. Most people pick up on the noise-gate stuff, which led to the NoNOISE work I did at Sonic Solutions (after many refinements, most of which are still proprietary so that I can't disclose them). What I consider the most important part of the paper is that the effect of certain families of window functions such as Hamming, Hanning, Blackman, or any that are finite sums of harmonic sinusoids can be calculated in closed form. I find this a remarkable result (although obvious in hindsite). If I want to divide the spectrum into 5, 10, 50, or 500 bands, I can compute linear-phase FIR impulse responses that will do that by evaluating formula (17). Note that the bands do not have to be equal-width. For instance, I could do something like a wavelet transform by having consecutive filters use wider and wider bandwidths. These will all sum to an impulse (by construction), so that they are guaranteed to be an identity. I know now that it is not limited to those window functions - that this can be done using any window function. That is, you can just write down the coefficients of the impulse responses of a set of filters that will divide the spectrum up any way you want. Maybe I should rewrite this paper sometime. Or maybe not.

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The Use of the Phase Vocoder in Computer Music Applications Journal of the Audio Engineering Society, Volume 26, Number 1/2, January/February 1978, pp42-45. This paper is one of the first (maybe the absolute first) to show how to use short-term Fourier transform as a method of analyzing and synthesizing musical sound, but with the signal-processing rigor necessary to make the system an identity in the absence of modification. Probably the most ignored contribution, and the one I consider probably the most important, is the technique for unwrapping the time-variant phase. Equation (9) represents a largely foolproof unwrapping method that involves no heuristics. This paper led to much of the subsequent work by Dolson and others who have extended and refined the method for time and frequency modification of high-quality musical sound.

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Signal Processing Aspects of Computer Music: A Survey Proceedings of the IEEE, Volume 65, Number 8, August 1977, pp1108-1137. This was an invited paper. Larry Rabiner invited me to write and submit this paper. It still stands as a reasonable survey of signal processing in music. It is interesting that synthesis is so little used today, whereas recording and playback (i.e., sampling) is so common. I guess it's a lot easier. Missing from this paper is any discussion of processing of the signal (aside from analysis). The computation for any interesting processing, except maybe reverberation, was so expensive at that time that we were not able to do much of it.

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About This Reverberation Business Computer Music Journal, Volume 3, Number 2, June 1979. This is a somewhat rambling random walk through some investigations into room reverberation. I had originally submitted it to the Journal of the Acoustical Society of America (JASA). I got a scathing review back that I swear was longer than the paper. The reviewer complained that it was in "an antequated discursive style." Yeah, that's probably correct. The reviewer differed with me on several technical points. I thought about it a while and concluded that the reviewer missed the point and didn't know what he was talking about, and in at least one area was flat wrong. Rather than try to fight with the reviewer, I sent it to CMJ, who was quite happy to publish it the way I wrote it.

I should mention that I believe I got mixed up between feet and meters in the graphs of air attenuation with distance. You may want to check this in a real acoustics textbook if it is important to you.

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On the Segmentation and Analysis of Continuous Musical Sound by Digital Computer Center for Computer Research in Music and Acoustics, Department of Music, Stanford University, Report No. STAN-M-3, May 1975. This is my doctoral dissertation at Stanford. My thesis advisor was Alan Kay. This is generally sited as the seminal work on transcription of music. That is, you play a piece (a duet, in this case) into the computer and some time later, it prints out a score. This proved very difficult, and especially with 1975 computer hardware (DEC PDP-10).

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On the Transcription of Musical Sound by Computer Computer Music Journal 1977. This is a reprint of a conference paper at the Japan computer conference earlier that year. I was unable to attend the conference (lack of travel budget). CMJ was kind enough to reprint the article later. This is a relatively brief summary of the work in my doctoral dissertation (above).

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The Use of Linear Prediction of Speech in Computer Music Applications Journal of the Audio Engineering Society, March 1979, Volume 27, Number 3, pp134-140. This paper was about the base technology for my early computer pieces "Perfect Days" and "Lions are Growing". This was building on the work of Charles Dodge, Tracy Petersen, and many others. It turns out to be quite difficult to synthesize speech, even given a recording that you use as a template. I got to revive these techniques when I did my piece "The Man in the Mangroves Counts to Sleep", but with modern computing techniques. In this paper, I was boasting that it "only" took 45 minutes to synthesize 30 seconds of sound(!). Note that many of the techniques outlined in this paper are still used today.

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The Use of Prime Residues as a Block Erasure Code with Linear Decoding Time Worldcom 2008. I include this paper mostly because I wanted to point out that I do things besides audio sometime. Plus, in case it needed a recommendation, to strongly advise engineers (audio or otherwise) to take all the math they can stomach. The innovation in this paper makes use of number theory, group theory, and statistical communication theory. I would probably not have done it without all that background. From the abstract ". . . prime residue encoding forms a non-systematic block erasure code that is asymptotically MDS (maximum distance separable) as the word size is increased. The uses for this code include digital fountain implementation, efficient payload distribution for digital watermarking, and more." This code related to Luby codes and "Tornado" codes. The big advantage is that the signal can be reconstructed from any N packets. If you miss one, you just copy one from your neighbor, even if it was encoded with a different set of primes.

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A Note on the Implementation of Audio Processing by Short-Term Fourier Transform WASPAA 2017. "Short-term Fourier Transform (STFT) forms the backbone of a great deal of modern digital audio processing. A number of pub- lished implementations of this process exhibit time-aliasing dis- tortion. This paper reiterates the requirements for alias-free pro- cessing and offers a novel method of reducing aliasing."
It is a wonderfun thing these days that people post MATLAB implementations of their research work. I was looking at audio source separation recently, and it was absolutely wonderful to just download their MATLAB programs and try them out. In the process of doing so, I was horrified to notice that they were all violating the most basic rule of fast convolution. They were doing the padding incorrectly (or not at all!) so as to create time-aliasing that was sometimes audible. This paper was an attempt to explain the proper way to do STFT analysis-synthesis.

Random Notes

I read somewhere that papers with a colon in the title attracted more attention and were

perceived as more athoratative, so I always tried to put a colon in each and every title for my

papers. I dunno if it worked or not.

There are some funny lines in these earlier papers. Since digital audio was in its infancy, I felt I

had to work real hard to convince people that these techniques were for real. That accounts

for statements like "[digital techniques] are currently being used in major motion picture

production." You don't have to say things like that any more.

I had other statements like "These techniques will have a major influence in

the all-digital studios to come." Today, these statements seem totally gratuitous,

since all the studios are digital, and the techniques are so

routine that nobody thinks about them any more. I guess that is how it is supposed to be.

I can't tell you how many people I had tell me that there is no way that we can do away with

all the analog equipment. One by one, I watched the analog pieces of equipment get replaced

by digital. Studios stopped asking "whither digital" and began asking "what will our approach to

digital be?" Nowdays, every garage band has a digital recorder, whether it is a free-standing

device or something running on a PC.

In "Signal Processing Aspects . . .", I describe digital recording and editing on the computer.

Although we weren't the first to do it - I believe Tom Stockham and Robert Ingebretson at

SoundStream antedated us by a few years - I think we were probably the second.

Some digital recording had been done at MIT and Bell Labs a decade earlier, but not for the purpose

of music editing. We could lay down up to 5 tracks before the sluggish hard drive of that era

started missing transfers.