Audio Level Meter for Maintenance and Adjustment of Studio Equipment
The CH711 is an audio level measuring instrument for the examination and maintenance of studio equipment. In connection with the audio generator CH709 a compact, multi-mode measuring and alignment system can be constructed That can be used to perform numerous, important measurements. Both modules have balanced and floating outputs and can process signal levels as high as +30dBu.
The level meter has a total of 5, switch selectable inputs. Inputs 1 and 2 are on XLR connectors and are located on the front plate of the device. Input 3 and 4 are accessed through two of the standard the XLR connectors on the mounting frame. Furthermore, there is an input for the connection of the generator, which is accessed on input 3 of the mounting frame.
The input of the measuring amplifier is balanced and can process signal levels as high as +36dBu in the frequency range between 20 Hz and 200 kHz. A 23 step stepped switch is used for setting the range. From -70dB to 0dB the level of the module can be switched in 5dB steps to +30dB. There are also two additional levels; -80dB and -90dB used for the noise measurements. Measuring values down to - 110 dB is possible.
The reference level of the meter can be changed by a level switch between 0 dBu for 0 dB and +6dBu for 0 dB. The unit can also be switched by another lever switch between calibrated operation and non-calibrated operation. In non-calibrated mode, the 0dB level is adjusted by the FLOAT pot in a range of ± 5 dB. This function is well suitable for comparison measurements.
Different weighted filters can be inserted. In the position OFF the measurement is unweighted with a bandwidth of 300 kHz. The frequency response is in the range from 10 Hz to 50 kHz is better than +/- 0.1 dB. In the position 22 Hz-22 kHz a band pass filter is activated which passes only this frequency band with 3 dB attenuation at the corner frequencies and a slope steepness of 24 dB/oct. In the dBA position the measurement scale is A weighted, and in the CCIR position, the CCIR 468-3 standard measurement filter is activated.
For the selective audio level measurement, there is a band pass filter with a band width of 1/3 octave. A 3 position, stepper switch selects the frequency range (20 Hz to 200 Hz, 200 Hz to 2 kHz and 2 kHz to 20 kHz) and the COARSE and FINE pots are used for detailed frequency selection.
The characteristics of the audio level meter can be changed with the MODE switch between AVG, RMS and QPEAK. In the position AVG a normal average value rectification takes place. In the position RMS the real RMS value is measured. Q-Peak switches the meter to display peak values, according to DIN45405.
The main output has an output voltage of 1V at full rated level and can be monitored with a headphone or an active loudspeaker. The second output with 0.1V output at full rated level is intended for the connection of an oscilloscope.
The CH711audio level measurement unit is a double wide module for installation in standard V700 mounting frames.