ÿWPCL ûÿ2BJ|xÐ ` ÐÐÌÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿH øÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÌÐÐ °°°è ÐÑ Âx„|ü@Ž ÑÐ Å@8Ø'@8Ø'Å Ð1.ÁHÁÓÓÃÃProposed revisions to Recommendation N.1ÄÄ Áà+ÁDEFINITIONS FOR APPLICATION TO INTERNATIONAL ƒ Áà3ÁSOUND©PROGRAMME TRANSMISSIONSƒ ÁàAÁƒ ÁàAÁƒ Ð Ð ÐÁHÁÃÃAddÄÄ 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". ÁHÁÃÃAddÄÄ the following new annex to Recommendation N.1: ÁàHOÁƒ ÁàHKÁ"ANNEX A*ƒ ÁàHDÁ(to Recommendation N.1)ƒ ÁàH9ÁÃÃLevel and loss units used for sound©programmeÄă ÁàHBÁÃÃand television transmissionÄă 1.ÁHÁÃÃUse of dB units in N RecommendationsÄÄ ÁHÁThis Recommendation gives the quantities and units for sound©programme transmissions used in N Recommendations and are in accordance with existing Recommendations [1], [2]. 2.ÁHÁÃÃUnits usedÄÄ 2.1ÁHÁÃÃAbsolute power level: dBmÄÄ ÁHÁAs 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. ÀÀÀÀÀÀÀÀÀÀÀÀ * It is intended that the text contained in this annex will be further studied   and refined as necessary. ÁHÁAbsolute 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. ÁHÁThe power level thus calculated would be equal to that measured in a correctly terminated system. 2.2ÁHÁÃÃRelative level dBrÄÄ ÁHÁThe 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. ÁHÁRelative 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. ÁHÁFor 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. 2.3ÁHÁÃÃAbsolute zero power level dBmO (load level*)ÄÄ ÁHÁIn a transmission system based on power levels the absolute power level or load level (LÃÃmoÄÄ) with respect to 1 mW is referred to a point of zero relative level. That means that the absolute power level (LÃÃmÄÄ) minus the relative power level (LÃÃrÄÄ) will be ÁHÁLÃÃmOÄÄ = LÃÃmÄÄ © LÃÃr ÄÄ ÁHÁThis 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. 2.4ÁHÁÃÃRelation between quantities and unitsÄÄ ÁHÁThere is a fixed relation between level quantities and units, namely: Absolute power level = relative power level + absolute zero power level (load level) ÁHÁLÃÃmÄÄ = LÃÃrÄÄ + LÃÃmOÄÄ Therefore, for the level units: a dBm = b dBr + c dBmO. ÁHÁWhen 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. ÁHÁLÃÃmÄÄ = LÃÃmOÄÄ À À À À LÃÃrÄÄ = O Ãà         ÄÄ *  The term "load level" is used provisionally and is subject to further    consideration. ÁHÁIn 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. 2.5ÁHÁÃÃWeighted levelÄÄ ÁHÁPower 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,Ô w.Ô (psophometric measurements), a "p" (for "pondÀ)ÀrÀ)À" = weighted) is added to the units, e.g.: dbmOp, dBmp. ÁHÁA "q" indicates a quasi©peak value where the "m" is replaced by a "q" which, for instance, in dBm gives dBq. 2.6ÁHÁÃÃExtra indicationsÄÄ ÁHÁSound©programme transmission level units are indicated by an extra "s" (s for sound), dBrs, dBmOs, dBmOps, dBqOpS. ÁHÁExtra 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.ÁHÁÃÃVarious measuring instrumentsÄÄ ÁHÁAbsolute power level (in dBm) is obtained if a measurement is made on a terminated line. ÁHÁVarious 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.ÁHÁÃÃPractical problemsÄÄ ÁHÁThere 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. ÃÃREFERENCESÄÄ [1] CCITT Recommendation B.12 "Use of the decibel and neper in     telecommunications". [2] CCIR Recommendation 574©2 under the same title."