514 Sound WavesSection 17.5Digital Sound RecordingSection 17.6Motion Picture Sound*P17.48For a 40-dB sound,4010101022212034310287 10128283dBdB±WmWmkg mm sW mN m22222=LNMMOQPP===×−−−−log..maxmaxIIPvPvI∆∆ρejbg(a)code =×=−28 765 53673..Nm22(b)For sounds of 40 dB or softer, too few digital words are available to represent the wave formwith good fidelity.(c)In a sound wave ∆Pis negative half of the time but this coding scheme has no wordsavailable for negative pressure variations.*P17.49If the source is to the left at angle θfrom the direction you arefacing, the sound must travel an extra distance dsinto reach yourright ear as shown, where dis the distance between your ears. Thedelay time is ∆tin vdt=sin∆. Then×=°−sinsin.116343210 1022 3vtd∆mss0.19 mleft of center.earearFIG. P17.49*P17.50103101012dBdB2=LNMMOQPP−logI(a)Ir=×=℘=℘−200 10
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