Nagra PORTABLE ANALOGUE AUDIO TAPE RECORDER Instruction Manual - page 50

METERING 

MODULOMETER OR V.U. METER 

To measure the level of an electrical signal representing a sound, there are two devices available, 

the modulometer and the v.u. meter. Both of them are voltmeters whose needle position represents 

the level. Their construction and use are however different. 

MODULOMETER 

The modulometer measures the peak value of the signal, irrespective of the form or the level, the 

modulometer takes into consideration the strongest positive or negative value. It is equipped with a 

memory, so the signal can be very brief, but the memory ensures that the meter needle advances 

and stays there for sufficient time for the operator to read it. The essential advantage of the 

modulometer comes from the fact that the measurement it gives is that which concerns magnetic 

recording, in other words it is the signal peak, which saturates the tape. The average value of the 

signal (as much as it concerns the listener) is of no importance to the tape. In particular, while 

recording noise, the modulometer indication is always exact, no matter how long the duration of the 

noise. 

The scale of a modulometer can be logarithmic, i.e. linear in decibels. In the case of the Nagra, it is 

possible, for example, to have a range of 70 dB. This allows the exact appreciation of even the 

lowest sound levels. Nevertheless, it is preferable to limit the range from  -30 to +5 dB, to help 

operators who are used to VU meters, which are not logarithmic. 

The operator, on seeing the needle move, knows that his level is greater than -20 dB.  

VU METER 

In the days of electronic valves (tubes), a modulometer was very costly, and the rudimentary VU 

meter was often preferred. Later, it was noticed that the VU meter still maintained a certain following 

and because of habit and standards many radio stations still use them.  

A VU meter is a simple rectifier voltmeter whose response time has been standardized. If the signal 

to be measured is continuous, (e.g. a whistle) the VU meter will indicate a value the same as the 

modulometer, but if the signal is intermittent (e.g.  speech) the VU meter will only indicate an 

average value, i.e. considerably lower than the instantaneous maximum levels. 

For speech, it has been found that this average value is approximately 8 dB lower than the peak 

value. By increasing the VU meter sensitivity by 8 dB, an indication of 0  VU. is obtained when the 

peaks reach the maximum value. This works relatively well in practice. For noise, the indication of 

the VU meter evidently becomes very inexact, and renders it practically useless. 

The v.u. meter, however, has certain advantages: 

a) 

Speech-music balance. If speech and music are recorded with a modulometer so that 

the peaks of the signal do not exceed the maximum level, subjectively the music 

appears stronger. This is due to the more continuous character of music signals. 

Therefore, in a mixed program, it is necessary to modulate the speech more strongly 

than the music. This can be done by modulating the music correctly and over 

modulating the speech or by under modulating the music. 

It is to be noted that a slight over modulation  of speech is not catastrophic: a 

transmitter is fitted with a limiter, as in the Nagra 4.2, which cuts peaks exceeding the 

maximum level. The subjective deterioration of the sound quality remains 

unnoticeable. On the other hand, a strong modulation increases the range of the 

transmitter and is of direct interest for commercial radio stations. 

A VU meter under indicates the speech. In modulating a program to 0 VU the speech 

will be over modulated and the music under modulated. From this point of view, the 

VU meter seems to be of more interest for mixed transmissions whose quality is not of 

great importance, but whose range should be as large as possible.