STANDARD VOLUME INDICATOR AND REFERENCE LEVEL 101 



not fast enough to indicate the instantaneous peaks of speech or 

 program waves but tend to average or integrate a number of peaks of 

 the wave. 



A feature of the usual peak-reading instrument which from the 

 analytical standpoint is of secondary importance, is that it is usually 

 given a characteristic of very slow decay as well as rapid response. 

 This is usually accomplished by a circuit such as illustrated in Fig. 2, 

 which shows the principle of the experimental instrument used in the 

 tests described later. The 0.01-mf. condenser is charged through a 

 full wave vacuum tube rectifier, the rates of charge and discharge 

 being determined by the resistances. The d.-c. amplifier and d.-c. 

 milliammeter indicate the charge on the condenser. The advantage of 

 making the discharge rate of the condenser very slow is that the d.-c. 



CONTROLS SPEED R2 



OF RESPONSE CONTROLS RATE 

 OF DECAY 



D-C 

 MILLIAMMETER 



Fig. 2- — Schematic diagram of experimental peak reading volume indicator. 



milliammeter need not then be particularly fast and, moreover, the 

 ease of reading the instrument is greatly increased. 



From the above analysis it is seen that the r-m-s and the peak- 

 reading instruments are essentially similar and differ principally in 

 degree. Both indicate peaks whose durations exceed some value 

 critical to the instrument and both average or integrate over a number 

 of peaks the shorter, more rapid peaks encountered in speech or pro- 

 gram waves. Either may have a linear or a square law detector, or 

 one of some intermediate characteristic. The important difference 

 between the two types lies in the speed of response as measured by the 

 length of impulses to which they will fully respond, that is, in the time 

 over which the complex wave is integrated. 



A general purpose volume indicator may be called upon to serve a 

 number of uses, such as: 



{a) Indication of a suitable level for a speech or program wave to 

 avoid audible distortion when transmitted through an amplifier, 

 program circuit, radio transmitter or the like. 



