Transfer Functions

The innovation of source independent measurement is not just that it displays the transfer function across any two points in the signal chain, but that it distinguishes the effects of each component, enabling you to tune the system to precisely what you want the audience to hear.

Frequency Response: Amplitude and Phase vs. Frequency

In Frequency Response mode, SIM 3 software displays amplitude, phase and coherence (or signal-to-noise ratio) data from the transfer function computations between any two of the measurement inputs. Unlike conventional audio analyzers that give you only part of the picture and leave you to draw your own conclusions, SIM 3 lets you see measurements using real program material, such as a live musical performance, in addition to showing you the results of internally-generated test signals like pink noise or a sine wave.

• SIM 3 software shows you exactly what is going on within the system in both frequency and time domains
• Ultra-flexible software alternates between viewing pertinent frequency spectra, impulse responses, and frequency response at key points in the system
• Measures and displays multiple transfer functions at the same time for thorough system analysis

By comparing the input and output signals of each component in the system, the system’s effect on the signal — the transfer function — can be obtained and displayed as frequency, phase response and signal-to-noise ratio.

3 is the Magic Number

A capability unique to the SIM 3 audio analzer system, these three transfer functions work simultaneously to provide real-time data acquisition. The SIM 3 system starts by measuring the effects of the electronic or acoustical signal path through a comparison of two points in the signal chain, most commonly combinations of the mixing console output, equalizer or digital signal processor output, and a microphone placed in the room to capture the sound as heard by the audience. Three transfer functions using state-of-the-art, dedicated hardware and software processing make possible a slew of computations and measurements, delivering a wealth of information in both frequency and time domains.

You can select three different frequency response measurement views:

• Room + Speaker – the unfiltered system response, measured by comparing the signal processor output and microphone
• Processor – the signal processor and inverse processor response, measured across the processor from input to output
• Result – the corrected system response, measured by comparing the processor input and microphone

Use the buttons at the top right of the figure to see SIM 3's three transfer functions showing frequency response in action.

In addition, you can select Group view to instantly see these three frequency response measurements at the same time. Zoom features can also be used to display the measurement with a different amplitude scale or a smaller range of frequencies to reveal fine details of the system response. In Group view the result is a crystal clear display of not only what is really going on acoustically, but the effects of each component identified by the SIM 3 analzyer in the system.

You apply the correction you need to obtain your desired frequency and phase response while the software measures the effects of your changes in real-time. Since the test signal is what you are actually hearing, analysis and correction can be performed dynamically throughout the course of an event. In contrast, traditional analyzers, using only pink noise or sine waves, cannot be used during the most critical phase of the sound system's work: the performance.

The SIM 3 Frequency Response group display. The lower pane shows frequency response of the speakers and room in white (processor output to microphone), processor curve in green (inverse trace shown), and signal coherence in red. The top pane shows frequency response for the whole system, or Result (console output to microphone) including the signal coherence also in red.

Simultaneous viewing of frequency responses throughout the system allows you to compare and understand the effects on the signal of the EQ or processor chain, the loudspeakers and room, or both (system response). Each transfer function is calculated and displayed at an unheard of resolution of 48 points per octave – double that of SIM II and other software-based analyzers. Smoothing functions can be applied to the display to show the data at lower resolutions, such as 1/6 or 1/3 of an octave.

All of this – blazing speed, ultra-high resolution and multiple simultaneous transfer functions – is possible because the SIM 3 analyzer uses dedicated processors for DSP and display.

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