THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA Volume 34 Number 6 JUNE. 1962 Quality of Piano Tones HARVEY FLETCIIER,E. DONNEL• BLACKHAM,AND RICIIARD STRATTON Brigham Young University, Provo, Utah (ReceivedNovember 27, 1961) A synthesizerwas constructedto producesimultaneously 100 pure toneswith meansfor controllingthe intensity and frequencyof each one of them. The piano toneswere analyzedby conventionalapparatus and methodsand the analysisset into the synthesizer.The analysiswas consideredcorrect only when a jury of eight listenerscould not tell which were real and which were synthetictones. Various kinds of synthetictones were presented to the jury for comparisonwith real tones.A numberof thesewere judged to have better quality than the real tones.According to thesetests synthesized piano-like tones were produced when the attack time was lessthan 0.01 sec.The decaycan be as long as 20 secfor the lower notes and be lessthan 1 secfor the very high ones.The best quality is producedwhen the partials decreasein level at the rate of 2 db per 100-cpsincrease in the frequencyof the partial. The partialsbelow middle C must be inharmonicin frequencyto be piano-like. INTRODUCTION synthesizer,and (4) the frequencychanger. To these HISpaper isa reportof our efforts tofind an ob- facilitieshave been added, a sonograph,an analyzer, a jectivedescription of the qualityof pianotones as single-tracktape recorder,a 5-track tape recorder,and understoodby musicians,and also to try to find syn- other apparatususually available in electronicresearch thetic toneswhich are consideredby them to be better laboratories.A block diagram of the arrangementis than real-piano tones. shownin Fig. 1. The usual statement found in text books is that the pitch of a tone is determinedby the frequencyof EQUIPMENT vibration,the loudnessby the intensityof the vibration, 1. Anechoic Chamber and the quality by the waveform.This picture is far too simplefor any of thesethree subjective aspects of a An anechoic chamber was constructed for use as a tone. Pitch and loudnesshave received very extensive listeningroom. It wasbuilt accordingto the architect's study. In this paper an attempt has been made to drawingsloaned to us by the Bell TelephoneLabora- throw some additional light upon the quality of a tories. Therefore, it is a copy of the one at those piano tone. laboratories. It is true that the quality dependsupon the wave- It consistsof a rectangularblock of cementwith in- form. But it alsodepends upon the pitch, the loudness, side dimensions of 40X30X30 ft. The block rests on the decayand attack time, the variationwith time of sand and gravel, and is completelyseparate from the the intensity of the partials, the impact noiseof the rest of the Eyring ScienceCenter building. The room hammer,the noiseof the dampingpedal, and alsothe was treated with 6-ft acousticalwedges on each side, characteristicending of the tone by the dampingfelt, thus reducingthe size 12 ft in each direction.A wire- etc. mesh floor was constructedby stretching steel wires In order to study the relative importance of these across the steel I-beams on the sides. These wires were variousfactors, the followinglaboratory equipment and separatedby 2 in., and there were two sets at right room facilities have been developed, namely, (1) anglesto each other. This resulted in meshes2 in. anechoicchamber, (2) loudspeakersystem, (3) tone square.The floor is 10 ft belowthe ceilingedge of the 749 Copyright ¸ 1962 by the AcousticalSociety of America. Redistribution subject to ASA license or copyright; see http://acousticalsociety.org/content/terms. Download to IP: 128.187.97.22 On: Fri, 14 Mar 2014 23:21:17 750 FLETCHER, BLACKHAM, AND STRATTON FREQUENCYSHIFTER TONE SYNTHESIZER PowerSupply The requirementsplaced upon the power supply i•0I [00ank;oo, - CPS I consistedof (a) supplyingadequate power at the ap- [ R . propriatevoltages and (b) maintenanceof a low level of noiseand hum. The secondof the two requirementswas Ampl tier themost difficult to •atisfy,and was especially difficult 'I in this casebecause of the surgesof power involvedin the operation of the attack and decay amplifier. To obtain this low noiselevel, a 6-v dc battery wasused for TAPE I RECORDER#1 the attack and decay amplifier vacuum-tubegrid and filament supplies, and for the transistor oscillators' power requirements.The use of this simple battery M icrcphone eliminatesthe inherent problemsposed by alternating Input • • TAPE current supplies.To obtain the requiredplate voltage swiTCH ING RECORDER for the attack and decay amplifier, a General Radio pwr.amp I •• _•-• 2high-frequency high-voltage supply was used in conjunction with I I • unit specially designedfilters. These filters consistedof :•- I •1• middle- R-C filter sectionsand voltage regulator tubes;it pro- ;_ duced a constant voltage output with a noise or "ripple" level 80 db below the output signallevel. Audio-FrequencyOscillators A CLUSTER OF 7 1S" SPEAKERS Since100 oscillatorswere required it was necessaryto selecta designwhich was compactand which gave a Fzo. 1. Block diagram of equipment. stable oscillation. This was accomplishedby using transistorswith printed circuits. The circuit elements acousticalwedges and 8 ft abovethe lowerset of wedges. were mountedon a panel board 5 in. long and 1« in. It will supportconsiderable weight but has little or no wide. The inductanceelement can be varied by turning reflectionfor any of the soundsin the audible range. a key which can be insertedin a small hole throughthe Chairs were supportedon this wire floor at one end of face of the panel. In this way each oscillatorcan be the chamberfor the jury of listeners.The loudspeaker turned to any desiredfrequency within about 1-octave systemwas installedat the oppositeend. range.The 100 oscillatorscan be tuned to covera range from 50 to 15 000 cps.These 100 smallpanels supporting 2. Loudspeaker System the oscillatorswere stacked together into three large This consistsof a three-channelsystem, each channel panels. Two of these large panels are shown at the transmitting, respectively,the bands of frequency20 bottom half of Fig. 4. The other panelis on the opposite to 400 cps, 400 to 4000 cps, and 4000 to 16 000 cps. sideof the portable table carrying the synthesizer. The low-frequencychannel consists of sevenAltec 803 B driversmounted close together in a circulararrangement Attenuatorsand Preamplifiers as shownin Fig. 1, with a bafflewhich was 8 ft square. The output of each oscillatoris sent through an at- This baffle was mounted so it could turn about a hori- tenuator and then to its preamplifier.The 100 atten- zontal axis. At certain anglesfrom the vertical, a more uatorswere arranged in a compactform at the back of a uniform responsefor the very low frequencieswas black panel board. White knobs (100 of them) which obtained. wereprojecting thro•tgh the blackpanel board and As indicatedin Fig. l, the medium-rangeloudspeaker which were connectedto the sliding contact of the wasa sectional-typehorn, and the high-frequencyloud- attenuator could be moved up and down in vertical speaker was of a tweeter type. The responseof this slots to control the amount of attenuation introduced system is given in Fig. 2. into eachoscillating circuit. Each attenuator covereda rangeof 50 db. They wereconstructed so that the down- 3. Tone Synthesizer ward movement of the knob producedan attenuation The tone synthesizerused to producethe synthetic tones consistedof five major parts, namely, a power supply, audio-frequency oscillators, a white noise [ ! .J-- i [ , i i , I ' sourceand filter set, attenuatorsand preamplifiers,and ;30•050 70 100 200 •00 500 1,000 ::',000 •.,000 '10,000 20,000 an attack and decay amplifier. A block diagram is FREQUENCY shownin Fig. 3. FIG. 2. Relative responseof loudspeakersystem. Redistribution subject to ASA license or copyright; see http://acousticalsociety.org/content/terms. Download to IP: 128.187.97.22 On: Fri, 14 Mar 2014 23:21:17 QUALITY OF PIANO TONES 751 I Sou: , ,. i HIGH VOLTAGE VOLTAG E ,, POWERSUPPLY F I LT ERS TACK& DECAY ' I WHILEN01SE DECAY FIG. 3. Block diagram for tone SUPPLYFILTERS AND synthesizer. 6.0 VOLT BAIIERY I I - AMPLIF IER I WHITENOISE OSCILLATORS CONTROL & PREAMPLIFIERS Swiich I' I" AUDIO 1Ameans of applying FREQUENCY attack and decay to OSCILLATORS some external source such as a continuous ATTENUATORS----•"PREAMPLIFIERStone tape recording. in db which was proportional to the distance it was by connectingthe battery voltage through a resistorand moved. A db scalewas engravedon the face of this capacitorseries circuit or shortingthrough the same panel.It is thus seenthat the relativepositions of these capacitorbut differentresistors. This functionis con- white knobsin vertical level give the relative levelsin trolled by a push-buttonswitch called the manual db of the current going from the oscillatorsto the controlswitch. The outputsignal will increasewhen the preamplifiersand showsgraphically the structureof the buttonis pushed,build up to its maximumvalue, and partials of the tone beingsynthesized. remainat that point until the buttonis released.Upon In the upper part of Fig. 4 this panel is shown.The release,the decaycircuit is in useand the decayingrate knobsin the picture are set to producethe synthetic is appliedto the signal.The rate of attackand decay is pianotone A"", the lowestnote on the piano. determinedby the adjustmentof the resistanceused in the R-C circuits.See Fig. 5. Attackand DecayAmplifier Anothercontrol used is the "dampingpedal" control