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The committee on Digital Signal Processing of the IEEE Group on Audio and Electroacoustics has undertaken the project of recommending terminology for use in papers and texts on digital signal processing. The reasons for this project are twofold. First, the meanings of many terms that are commonly used differ from one author to another. Second, there are many terms that one would like to have defined for which no standard term currently exists. It is the purpose of this paper to propose terminology which we feel is self-consistent, and which is in reasonably good agreement with current practices. An alphabetic index of terms is included at the end of the paper.

The primary aim of this work has been to develop a stereophonic system for recorded music, using a small, inexpensive and practical cartridge with magnetic tape as the information carrier. In order to make the cost of the recorded cartridge comparable with a disk containing an equivalent amount of music, it was realized that basic developments in magnetic recording such as efficiency of recording and reproducing techniques were necessary to meet the packing density requirements. This paper describes developments which have led to a recorded cartridge one fifth of the volume of a disk and capable of playing more than one hour of stereophonic sound uninterrupted. In order to obtain the desired signal-to-noise ratio and frequency response to 15 kc, radical improvements have been made to tape, recording system and playback head. In conjunction with this work, a fully automated tape machine has been developed. The machine is equipped with a changer-type mechanism and accommodates a number of cartridges which are played and rewound completely automatically, one after another, furnishing music for several hours. The machine requires no manual threading and has a rewind cycle of less than twenty seconds for an hour-long tape.

The material presented in this paper gives a selection of "ready-made" triode cathode-follower circuits applicable to the problems of impedance matching to audio filters and transformers. Curves resulting from breadboard tests are given on five tube types, and illustrative examples are included.

At the helm of G-AE publications since 1965, Mr. Frederick Van Veen, of Teradyne, Inc., Boston, Mass., recently requested to be relieved of his duties as Editor-in-Chief because of increasingly conflicting demands being placed on his time. We owe him a great debt of gratitude for his invaluable contributions toward revitalizing the Group's TRANSACTIONS. Under his leadership, the TRANSACTIONS pages published annually increased over 250%. This growth has not been at the expense of quality; on the contrary, the Group has published many truly significant papers and has become a forum for reports of new work in the exciting field of digital signal processing. Evidence of this fact is the run on some special issues, especially those devoted to digital signal processing. Incidentally, an anthology of the best papers on digital signal processing, currently in preparation, will rely largely on papers published in the G-AE TRANSACTIONS. Owing in no small part to Mr. VanVeen's organizational talents, the TRANSACTIONS now receives a steady supply of high-quality papers. But this makes it more difficult to schedule special issues without holding up publication of accepted papers. In view of the importance of special issues, then, the Group is moving in the direction of changing the publication schedule from quarterly to bimonthly. Dedicating the additional issues to special topics will, in effect, allow us to meet the demands for special issues without lengthening the interval between regular issues. We expect that this scheduling change will help us serve our membership better. The turnaround of the TRANSACTIONS is based on the relentless effort of a dedicated few, of which Mr. VanVeen has been a key member. On behalf of the Group on Audio and Electroacoustics, I want to express my sincere appreciation for all of his accomplishments in carrying out the demanding task of Editor-in-Chief. We welcome Mr. William E. Collins, of General Radio Company, Concord, Mass., who has assumed the post of Editor-in-Chief.

Consideration of the scope of the items in the PGA Briefs section of this issue should prove impressive not only because of the diversity of organizational activity in the audio field, but because of the comprehensive publication effort to provide thousands of engineers and scientists, in various organizations both here and abroad, with the information required for advancemenotf audio engineering and technology. This issue starts the third official volume of regularly scheduled IRE-PGA publication. The majority of the papers published so far have been written by people with considerable previous experience as technical authors. Yet quite a few papers of technical competence, even excellence, have been contributed by younger authors. The new awards system soon to be inaugurated will provide additional recognition and awards for outstanding authors in each of these categories.

The July, 1955 issue of the 'Journal of the Acoustical Society of America' contains 24 papers on Acoustics and Audio. Five of these, thought be of special interest to the members of the IRE Professional Group on Audio, are abstracted here. Additional articles of interest are also noted.

This Paper presents a useful "handbook type" equation for calculating a suitable self-bias resistor for a class A triode amplifier stage designed for maximum signal output. It is shown also that the loss in gain is six decibels, when the cathode resistor is not shunted by a by-pass capacitor. This information provides a timesaving method for determining the cathode resistor, with only a knowledge of plate resistance and transconductance, and without the necessity of a family of plate characteristic curves.

An error in calculation has been brought to our attention by Clifford E. Berry of the Consolidated Engineering Corporation, Pasadena, CA, USA. The error appears in Fig. 4 of the paper, "Lipstik Condenser Microphone System," by J.K.Hilliard and J.J. Noble, on page 165 of the November-December, 1954 issue of TRANSACTIONS OF THE IRE, vol. PGA-2, no. 6. The correction has been made in a drawing showing open circuit RMS voltage produced by thermal agitation in the real component of the impedance of a parallel resistor and condenser, which should be substituted for the original Fig. 4.

The author of the paper "Triode Cathode-Followers for Impedance Matching to Transformers and Filters," which appeared in the TRANSACTIONS OF THE IRE, the March-April issue, 1955, has drawn attention to the following omissions in the text. In Figs. 7-17 (pages 31-36), the titles which identify the tube types were inadvertently deleted. It is suggested that readers who anticipate use of these curves pencil the appropriate identification onto the figures. They should read as follows: Fig. 7-1/2-12AC7 '(B" (except for GAIN, which is for 1/2-12AX7 "B"), Fig. 8-1/2-12AT7 "A," Fig. 9-1/2-12.4T7 "B," Fig. 10-1/2-12AU7 "A," Fig. 11-1/2-12AX7 "B" (except for GAIN, which is for 1/2-12AU7 "B," Fig. 12-1/2-6BL7 "A," Fig. 13-1/2-6BL7 "B," Fig. 14-6AQ5 "A," Fig. 15 - 6AQ5 ("B," Fig. 16-12AU7 "A" (both halves in parallel), Fig. 17-12AU7 "B" (both halves in parallel). Note that because of the interchange of the GAIN data of Figs. 7 and 11, some of the data required in Example (1) of the text will be found in Fig. 7.