stimulus: Ability to generate different waveform types Sine Square Multitone (a group of simultaneous sine waves) Sweep (move continuously from one specified frequency to another) Standard Inter-modulation waveforms (SMPTE, DIN, DFD, and DIM) Arbitrary waveforms Extremely low residual distortion and noise Sufficient range of amplitude Sufficient range of frequency Extremely high accuracy of amplitude Extremely high accuracy of frequency Adjustable and accurate source impedance Balanced/unbalanced output options (analog) AC and DC coupling Additionally, the generator will allow for the definition of a precise frequency range and amplitude of the stimulus presented to the DUT. This is critical when aligning test conditions to the characteristics of the DUT. Signal Analyzer Prior to the introduction of integrated audio analyzers, audio generators and audio analyzers were separate pieces of equipment. In this article, signal analyzer refers to the element of a modern audio analyzer that implements the actual measurements. Whether realized in analog circuits, digital signal processing (DSP) or FFT, the analyzer engine must provide high precision implementations of: AC/DC voltmeter (peak and RMS) High pass, low pass and weighting filters Band pass and notch filters Frequency counter As most modern instruments are digitally based, signal analysis is frequently performed using FFT-based calculations, allowing many results to be calculated in a single test pass. Results of these measurements are processed by the analyzer into readable data using a variety of standard units and formats, such as volts, dB, dBu, SPL, ohms, relative percentage, etc., depending upon the specific measurement being reported. Derived results are achieved by combining several primary results into a calculated result. Measurements and Results Audio analyzers are capable of measuring many types of parameters. The fundamental measurements are: Level and gain: Level describes the magnitude of a signal, and may be expressed in absolute or relative terms. Common absolute units may be volts, watts, dBV and dBu, while relative measurements are expressed most commonly in dB. Level may also be conditioned as a peak measurement or an RMS measurement. Gain is the ratio of signal level at a DUT's output divided by the signal level at the input, usually expressed in dB. Frequency response: measures the output level of a DUT as a function of frequency. Level is expressed in the same units as above, typically dBV and dBu. Total Harmonic Distortion plus Noise (THD+N): Harmonic distortion products are multiples of stimulus frequencies, while noise is energy that is mathematically