2002 July/August, Vol 50 Number 7/8

CONTENT

PAPERS

On the Design and Efficiency of Class A, B, AB, G, and H Audio Power Amplifier Output Stages
Rosalfonso Bortoni, Sidnei Noceti Filho, and Rui Seara   547
Audio power amplifiers are usually analyzed with resistive loads with an added compensation factor for nominally reactive loads of real loudspeakers. The current study examines amplifiers of class A, B, AB, G, and H under conditions of reactive loads with sine wave to determine the true stress on the power stage. By using a more exact method, the economic inefficiency of the older approximation is avoided. A procedure for designing and assessing output stages is also proposed.

Requirements for Low-Frequency Sound Reproduction, Part I: The Audibility of Changes in Passband Amplitude Ripple and Lower System Cutoff Frequency and Slope
Søren Bech   564
The low-frequency loudspeaker in a 5.1 system has been investigated in terms of perception of its frequency cutoff, slope of the cutoff, and passband ripple. The cutoff frequency has a very significant effect on the subjective sense of "lower bass," but the cutoff slope was found not to be significant. The audibility of ripple depends on the nature of the audio signal. Results were consistent in both an anechoic test procedure and a headphone simulation of that environment.

ENGINEERING REPORTS

Requirements for Low-Frequency Sound Reproduction, Part II: Generation of Stimuli and Listening System Equalization
Jan Abildgaard Pedersen and Aki Mäkivirta   581
Using headphones to simulate the perception of loudspeakers in an anechoic chamber is easier and more efficient, but it requires signal processing to produce the equivalent sound signals. This study describes the algorithms used in a previous study of the low-frequency channel loudspeaker. Signals were pre-equalized with added nonlinear processing based on head-related transfer measurements made in an anechoic chamber with an actual loudspeaker.

Reconstruction Method for Missing or Damaged Long Portions in Audio Signal
Ismo Kauppinen and Jyrki Kauppinen   594
Using a reconstruction method described previously, the authors demonstrate an algorithm that replaces gaps of up to several thousand samples with synthesized audio. Using three different types of music, the extrapolation method was able to reconstruct successfully the missing audio, so that listeners could not hear the difference between it and the original. The method was applied in practice to correct scratches from badly damaged recordings, but it can also work with any kind of impulse noise in real time.

STANDARDS AND INFORMATION DOCUMENTS

AES Standards Committee News   603
Acoustics and sound-source modeling
Call for Comment on REVISION of AES10-1991(r1997), AES recommended practice for digital audio engineering-Format for the user data channel of the AES digital audio interface   603

FEATURES

113th Convention Preview, Los Angeles   606
     Calendar   608
     Exhibitors   610
     Exhibit Previews   614
Updates and Corrections to the 2001/2002 International Sections Directory   636
23rd Conference, Copenhagen, Call for Papers   641

DEPARTMENTS

News of the Sections   629
Upcoming Meetings   634
Sound Track   635
Advertiser Internet Directory   635
Membership Information   637
In Memoriam   639
Sections Contacts Directory   642
AES Conventions and Conferences   648

FPO For the cover:

2002 July/August, Vol 50 Number 7/8

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