Audio Application Notes
Measuring Mic-Preamp Noise
By Allen H. Burdick
To perform valid noise level measurements, two specific conditions must be established:
- A 150 Ohm source impedance
- A 20 kHz measurement bandwidth
The microphone preamplifier must have the proper source impedance at its input. If it does not, the preamp will amplify the noise of its internal bias resistors, resulting in much higher noise voltage. Typically, the easiest way...
Building the L-R Null Test Set
By Allen H. Burdick
In the process of broadcast matrix encoding and decoding, balancing amplitudes between the two channels of a stereo audio path is very necessary. It is necessary for the maintenance of proper headroom, dynamic range and, of course, separation.
From time to time, repair and maintenance must be performed on equipment. Returning the entire chain to a balanced condition when placing the equipment back in service, is very desirable. Most broadcast engineers have balanced a chain at the stereo generator using the L-R method. But why not balance the output of each piece of equipment throughout the studio and eliminate the trip to the transmitter? It could mean eliminating late nights, and for those who don't go off the air, it may be the only option.
While recording studios do not face the same problems as the broadcaster, much of what is recorded in a studio is broadcast. This technique, therefore, is also applicable to the maintenance of a final stereo path in a recording facility.