Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!linus!philabs!cmcl2!harvard!talcott!panda!teddy!rdp From: rdp@teddy.UUCP Newsgroups: net.audio,net.auto Subject: Re: Phase distortion on music Message-ID: <2159@teddy.UUCP> Date: Mon, 24-Feb-86 11:03:41 EST Article-I.D.: teddy.2159 Posted: Mon Feb 24 11:03:41 1986 Date-Received: Wed, 26-Feb-86 20:19:11 EST References: <1582@emory.UUCP> <523@eneevax.UUCP> <445@unccvax.unccvax.UUCP> <281@twitch.UUCP> Distribution: net Organization: GenRad, Inc., Concord, Mass. Lines: 88 Xref: linus net.audio:7148 net.auto:8598 In a recent article, George Tomasevitch asserts: > > The human ear is insensitive to phase and will not be affected by phase > distortion, provided the amplitude vs frequency characteristic is not altered. > The RIAA equalization for records produced horrendous phase shifts > at some frequencies, but we don't care. We do speech processing here, > so we are aware of what one can do to speech, at least. Some people in > this department have done 'hi fi' coding, too. The cheap amplifiers have > other problems, probably including intermodulation distortion. > -- Sorry, Mr. Heyser [1][2][3], sorry Mr. Fincham [4], sorry Mr. Lian [5], sorry Herr Linkwitz, sorry Messrs. Lipshitz, Pollock, and Vanderkooy [6] and sorry to all those once capable researchers who had determined that many kinds of phase shift are audible, Mr. Tomasevitch has, with the flourish of keyboard, made the ear "insensitive to phase". Poor phase, ears are no longer sensitive to it! The example given, "RIAA equalization for records introduces horrendous phase shifts at some frequencies, but we don't care" is ill chosen and an obvious red herring. First of all, the RIAA equalization does not produce "horrendous" phase shifts, as the absolute magnitude of the phase shift never exceeds 90 degrees (no more than one pole or zero in effect at any one time). Secondly, Note that the phase errors introduced should be the exact opposite of those impressed on the signal by the RIAA pre-equalization and playback characteristics of the reproduction system. The result is a net phase shift of 0 degrees across the audio band. Hence, the reason we don't care about phase shift in RIAA networks is because there shouldn't be any! Much speech processing is done using mere spectral energy vs. time and, in these measurements, phase is indeed not an issue (although I shan't pretend to tell Mr. Tomasevitch about his business, as he MAY know more about it than I). He may well be correct, in a very limited context, but 50 years of psycho- acoustical research indicates that phase distortion is quite audible. Certainly such a blanket pontification such as "the ear is insensitive to phase" falls flat on its face in light of the well-demonstrated fact that the ear needs very accurate phase information at midrange frequencies to localize apparent sound sources [7] (this is how stereo works!). I might be willing to swallow a statement such as, "Under the conditions of high noise levels, ambiguous reverberent fields and lacking the ability to sit in an optimum position, as found in an automobile, and given the lack of attention of the vast majority of radio stations and recording companies to issues such as phase, and given that many car stereo systems have speakers that have terrible phase characteristics, especially given typical placement, I feel that other anomolies in the reproduction system may have more significance than phase." Dick Pierce But a few references: [1] Heyser, R. C., "Loudspeaker Phase Characteristics and Time Delay Distortions," J. Audio Eng. Soc., Part I - vol. 17, no. 1, pp. 30, 1969 Jan., Part II - vol 17, no. 3, p. 130, 1969 Mar. [2] Heyser, R. C., "The Delay Plane, Objective Analysis of Subjective Properties," J. Audio Eng. Soc. Part I - vol. 21, no.11, pp 609- 701, 1973 Nov., Part II - vol. 21, no. 12, pp. 786-791, 1973 Dec. [3] Heyser, R. C., "Determining the Acoustic Position for Proper Phase Response of Transducers," J. Audio Eng. Soc., vol. 32, no. 1, pp. 23-24, 1984 Jan. [4] Fincham, L. R., "The Subjective Importance of Uniform Group Delay at Low Frequencies," J. Audio Eng. Soc., vol. 33, no. 6. pp. 436-439, 1985 June. [5] Lian, R., "Is Linear Phase Worthwhile?," presented at the AES Conv., 1981 May, preprint no. 1732. [6] Lipshitz, S. P., Pollock, M., and Vanderkooy, J., "On the Audibility of Mid-Tange Phase Distortion in Audio Systems,", J. Audio Eng. Soc., vol. 30, no. 9, p. 580, 1982 Sep. [7] Moir, J. "Speaker Directivity and Sound Quality," Wireless World, vol. 87, no. 1541, pp. 32-38, 1981 Feb.