Showing papers in "Journal of The Audio Engineering Society in 1968"

Modulation Distortion in Loudspeakers

Abstract: When comparing a loudspeaker with direct radiator bass system to one with horo loaded bass, the subjective judgment is that the one with the horn loaded bass is "cleaner". The difference in listening quality appears to be due to modulation distortion. The mathematical analysis of modulation distortion is reviewed and spectrum analyzer measurements are described which have been correlated with listening tests The spectrum analyses corroborate the mathematical analysis and the listening tests offer a subjective evaluation. It is concluded that frequency modulation in loudspeakers accounts in large measure for the masking of "inner voices". Reduction of diaphragm excursions at low frequencies reduces FM distortion. Horn loading, properly applied, offers greatest reduction, while simultaneously improving bass power output capability.

Speed, Pitch and Timing Errors in Tape Recording and Reproducing

Abstract: Because tape is a plastic medium driven by a capstan in a complicated rolling process, an accurate specification of “tape speed” is not simple. However, it is shown that even a complete specification of tape speed alone is not adequate to specify the pitch and timing error because changes of the recorded wavelength due to tape length changes cause additional independent timing and pitch errors of up to 1.0 %. These are significant in comparison with the NAB tape speed tolerance of ±0.2 %. Measurement techniques are also reviewed.

An Estimation of Annoyance Caused by Dropouts in Magnetically Recorded Music

Abstract: Both audibility and subjective appreciation of dropouts in magnetic recordings of music were estimated in a series of listening experiments in which the most vulnerable situation was simulated: the type of music, the playback conditions as well as the highly discriminating listeners cooperated to yield high annoyance ratings. In this way -worst case- (or True High Fidelity) criteria have been obtained.

A Simple Method for Phase Compensation in Tape Copying with Identical Tape Recorders

Abstract: pensation for phase distortion which wards via the playback head.amplifier signal is played back in the forward ordin.arily occurs in the audio tape combination of tape unit a with fredirection on tape unit b. The resultant record-playback process for the purquency characteristic Call(to)eJqba_(w). output voltage is pose of improving the fidelity of reThe resultant output voltage is Vo(jto) = (4) corded tran.sients, especially after Vl*Cae-J¢._Ca-lei¢_2 = (2) ----V1Coe--J(Oa_--e_+¢bOCb--_e_eb_ several.-re-recordings (dubs) of origiV_*g(¢_-¢,0. = .V_(jto)eJ(¢b_--¢,2+¢,_--eb_). n,al tapes. _ Therefore, attention should This signal is simultaneously recorded If tape units a and b are identical, the be called to an extremely simple on ta.pe unit b, and the flux recording record and playback phase shifts of method for making Phase-equalized on tape is equivalent to unit a are cancelled by those of unit dubs using two identical tape recorders V_*eJ(¢_-e,OCb(_o)ei_ = (3) b. That is, if which do not employ phase compenVi*C_eJ(_,_-¢*_+_,). qb_z= qbbl= qbland qba2= qbb2= (po, sation. This is accomplished by playing the original tape backwards during recording. The possibility for near-perfect v,(t) TAPEUNiTa RECORD AMPLIFIER (_a=Vicejqbl phase compensation depends on the (t) c _ o HEAD fact that the Fourier transform of a v,(joJ) cei_J time-reversed signal is the complex conjugate of the sigr_al in forward time. This is expressed mathemati -

Splicing Tapes and Their Proper Application

Abstract: An ideul splice is one that, when properly made, will remain intact for an indefinite period of time. Its mechanical strength is the first consideration, but there are other areas that may be counted lust as important. There must be an absolute minimum of \" ndbesice escape \" around the edge of the pmsswe sensitive tape used to make the splice, and the splice itself must not cause an audible disturbance on playback. With these three busic considerations in mind, let's investigate the factors and precautions that become part of the design of a splicing tape by the manufacturer and the fundmnentul r&s and possible pitfnlls with which the operator must be concerned. DESIGN REQUIREMENTS When designing in!, pwss~~r~ sensitive tape, the two obvious compownts :LW the. backing and the adhesive coating. In the d(~v(,lopmcnt of n tape suitable for split-ing magnetic recrrrclill,+ both of these components WPK' chosen with great ('ilrr. The backing had to 1)~ twlgh and durable while being as thin as possiblr. For this reason, paper was not snit-able; and plastic w~u chosen. Both acetate and polyester are currently bring 11w1. Developing an adhc%vc coating suitable for splicing tape was even mow involved. Here, three basic qualities must be carefully ,whl:~trd. These are known as (1) shear adhesion. (? 1 ~IY,I back or ASTM adhesion, and (3) thumb aplx~l. Shear adhesion can Ix: defined as the adhesive's resistance to being partrd from the surface to which it is adhered when pulled in what is commonly called the shear direction. Figure 1 demonstrates this by showing a piece of splicing tape being tested for its shear strength. Peel back or ASTM adhesion is, as its name implies, a measure of the adhesive's resistance to being peeled away from the surface to which it is adhered. Figure 2 graphically demonstrates how this test is performed. Thr next property is \" thumb appeal \" or \" quick stick. \" It is the quality of the adhesive to actually feel sticky. Oddly enough, it is not a particularly important quality as far as the strength of the bond is concerned, but it is a q~ulity that is readily noticeable to the user. There srems to be an \" old wives' tale \" that has led some users to believe that \" the stickier it feels, the better it will hold. \" This is not necessarily true when talking about splicing …

Electronic dummy for acoustical testing

Abstract: Electronic Dummy /ED/ used for acoustical testing represents the average male torso from the Xiphoid process upward and includes an acoustic replica of the human head. This head simulates natural flesh, and has an artificial voice and artificial ears that measure sound pressures at the eardrum or the entrance to the ear canal.