1.Proposed revisions to Recommendation N.1

         DEFINITIONS FOR APPLICATION TO INTERNATIONAL 
                 SOUND-PROGRAMME TRANSMISSIONS
                                
                                
       Add at the beginning of Recommendation N.1, an additional  reference  2)
to the title of the Recommendation which refers to the following footnote:

"2.  Annex A to this Recommendation gives definitions for units of measurements 
     for sound-programme transmissions".

       Add the following new annex to Recommendation N.1:  
                                       
                                  "ANNEX A*

                           (to Recommendation N.1)

                Level and loss units used for sound-programme
                         and television transmission


1.     Use of dB units in N Recommendations

       This Recommendation gives the quantities and units  for  sound-programme
transmissions used in N Recommendations and are  in  accordance  with  existing
Recommendations [1], [2].

2.     Units used

2.1    Absolute power level: dBm

       As a general rule, the dBm unit applies to the absolute power level. The 
unit is based on the ratio between measured power and the reference power of  1
mW.

















ÄÄÄÄÄÄ

* It is intended that the text contained in this annex will be further  studied
  and refined as necessary. 
       Absolute voltage levels, for which terminal impedance  is  not  defined,
are more rarely used. As a  correction,  power  level  may  be  calculated  for
impedances other than 600 ohms, with respect to 1 mW.

       The power level thus calculated would be equal to  that  measured  in  a











correctly terminated system.

2.2    Relative level dBr

       The relative power level of a point in  a  transmission  system  is  the
nominal power gain at the reference frequency from a reference point to the point 
considered. The same consideration is used for the relative voltage level in  a
transmission system based on voltage levels.

       Relative levels can be used to compare two or more points of  a  network
with respect to power (or voltage). One point of a network is usually defined as 
the reference point at 0 dBr, from which other measurement points are derived.

       For sound-programme circuits, the zero relative level is located at  the
injection point, i.e. usually at the transmission point  of  a  sound-programme
circuit.

2.3    Absolute zero power level dBmO (load level*)

       In a transmission system based on power levels the absolute power  level
or load level (Lmo) with respect to 1 mW is referred to a point of zero relative 
level. That means that the absolute power level (Lm) minus the  relative  power
level (Lr) will be

       LmO = Lm - Lr 

       This level indication is independent of the relative power level at  the
measurement point considered. For a given signal the load level is nominally the 
same along a transmission line. For this indication it is necessary to know  to
what extent the power at the zero relative point is greater or  less  than  the
reference power.

2.4    Relation between quantities and units

       There is a fixed relation between level quantities and units, namely:

Absolute power level = relative power level +
                       absolute zero power level (load level)

       Lm = Lr + LmO

Therefore, for the level units: a dBm = b dBr + c dBmO.

       When indications are given concerning the line signal, the absolute zero 
power level (load level) (dBmO) is given, at which, at the relative zero point, 
the absolute power level coincides with the relative power level.

       Lm = LmO  ³
                   ³  Lr = O

          

*  The term "load level" is  used  provisionally  and  is  subject  to  further
   consideration.

       In order to simplify the specification of the level of a  circuit  or  a
system it is most appropriate to specify the absolute power level which coincides 
with the relative zero power level. Thus this  absolute  power  level  and  the
absolute zero power level (load level) are the same.

2.5    Weighted level







       Power level of disturbing signals are as a rule expressed  in  the  same
units as those defined above. For noise measurements made by a weighting filter, 
(psophometric measurements), a "p" (for "pond‚r‚" = weighted) is added  to  the
units, e.g.: dbmOp, dBmp.

       A "q" indicates a quasi-peak value where the "m" is replaced  by  a  "q"
which, for instance, in dBm gives dBq.

2.6    Extra indications

       Sound-programme transmission level units are indicated by an  extra  "s"
(s for sound), dBrs, dBmOs, dBmOps, dBqOpS.

       Extra indications for units should  be  used  whenever  they  facilitate
understanding so as to prevent confusion when differing measurement techniques, 
weighting filters or meters are used.

3.     Various measuring instruments

       Absolute power level (in dBm) is obtained if a measurement is made on  a
terminated line.

       Various measuring instruments provide measurements related to a (freely) 
preselected relative level value. The measurement will  then  directly  express
the absolute zero power level (load level).

4.     Practical problems

       There is a  wide  range  of  measuring  instruments  used  at  different
measurement points, so that differences are always bound to appear. A state which every 
administration is prepared to define is  the  permitted  maximum  level  (PML).
Despite different relative power levels, depending on the systems, a direct relation 
can now be indicated between the value of the level to be measured and the  PML
in dB. If, for instance, a signal of 21 dB below the PML is  transmitted  as  a
measurement signal, it must also be received as  a  signal  21  dB  below  PML,
independently of local relative levels, which may differ according to systems and 
administrations.

REFERENCES

[1]  CCITT  Recommendation  B.12   "Use   of   the   decibel   and   neper   in
    telecommunications".

[2] CCIR Recommendation 574-2 under the same title."