The Ivie IE-30 is the industry standard, hand held Audio Spectrum Analyzer. Bexel has these for rent. Years ago, before technology was small enough to build something like the IE-30, acoustic analysis came in the form of a single VU-meter device that could measure only one frequency at a time. To analyze an entire spectrum (low to high), single frequencies were generated by he sound system and the analyzer was set to measure the single frequency. To generate a plot of the room, as many as thirty frequencies were individually generated and measured. This was very slow, and prone to error. The greatest short coming of this method was, however, that the relationship between frequencies could not be identified because only one frequency was ever measured at a time. When true Spectrum Analyzers were developed, the ability to analyze all frequencies at one time was referred to as "Real-Time-Analysis", and hence the audio industry nomenclature of "RTA" to describe the device. RTA's use a test signal called Pink Noise. This broad-band signal contains a collection of many frequencies as does speech or music program material. The combination of frequencies allows the engineer to determine how the acoustics of the venue would effect the program material. The IE-30 kit comes with an external noise generator. Most larger PA audio consoles have a built in noise generator.

RTA's are used to analyze "Acoustic" energy. Acoustic energy generally comes from two sources:

• Ambient noise such as air-conditioning rumble, or machinery
• Sound system generated energy either as music or a calibrated test signal

In addition to analyzing the volume of individual frequencies, the Real-Time-Analyzer can also indicate Sound-Pressure-Level or SPL, which is used by OSHA and other monitoring organizations for industrial and entertainment health purposes.

More to come... (See Sound Advice Number 150)