What is SIM 3?
SIM 3 is a dedicated computer measurement instrument that implements Meyer Sound's Source Independent Measurement (SIM®) technique. SIM uses the program material as a reference to accurately compute the transfer function (amplitude and phase response) of a hall or speaker system. It thus permits measurements using music.

SIM 3 displays data on a high-resolution color video display. Curves can be stored in computer memory for fast comparative analysis, or archived to the SIM 3 Analyzer's internal hard drive for post-processing. Separate display "pages" permit analysis of the transfer function (amplitude and phase in the frequency domain), spectrum (amplitude in the frequency domain) and calculated impulse response (amplitude in the time domain).

Data are taken by the following procedure. Up to 64 calibrated measurement microphones are deployed throughout the space in suitable positions. Connections also are made at the inputs and outputs of the system equalizers, allowing the operator to measure each equalizer's response individually. The mix console output is connected to the SIM 3 Analyzer as the measurement reference.

What are the advantages of SIM 3 over conventional FFT analyzers?

Accuracy: — The SIM 3 employs 32-bit floating-point Digital Signal Processing (some operations are calculated with 64-bit precision), affording ±0.1 dB amplitude accuracy. This represents the state-of-the-art in audio frequency measurement.

The SIM 3 Analyzer's "smart averaging" routines (which perform RMS or vector averaging on a per-frequency-bin basis), coupled with proprietary thresholding functions, assure that only accurate data (i.e. measurement-channel data for which a causal excitation is present) are displayed. Other analyzers display data even if there is no causal excitation signal, relying upon the operator to discriminate between valid and invalid readings.

Speed: — The SIM 3 is over ten times faster at data acquisition, display and storage than competing units such as the Bruel & Kjaer models 2032/2034 or Hewlett-Packard models 3582A/35660A Spectrum Analyzers.

Power: — To achieve performance equivalent to SIM 3 v. 2.0, up to nine HP model 3582A Analyzers, running in parallel under external computer control, would be required. v. 2.3 Multi-Channel could only be equaled by twenty-seven 3582A Analyzers in parallel.

Efficiency: — SIM 3 allows you to gather amplitude and phase response data faster and with greater accuracy, than any other audio analyzer on the market. Its Delay Finder function provides an extremely fast and accurate method for setting external delays to align fill systems in minutes - rather than hours.

Flexibility: — Source Independent Measurement permits use of non-Gaussian noise, sine wave sweeps or other excitations to build a valid transfer function. (The SIM algorithms assume that the object of measurement has a stable transfer function during the measurement period). Conventional dual-channel FFT analyzers require an impulse, or periodic or Gaussian noise excitation, to achieve equivalent amplitude accuracy; when music is the test signal, their accuracy is no greater than between ±0.5 and ±1 dB.

Explain the hardware/software version of SIM 3 System that Bob Hodas uses?

In v. 2.3 Stereo, the SIM 3 employs a single DSP card and has no provisions to accommodate SIM 2403 Interface Networks. It is designed for efficient single-microphone testing and equalization of multi-channel sound theater systems and recording studio control room monitors.

In situations where there are not time constraints, the SIM 3's extensive data storage capabilities allow testing of complex, multiple-branch sound systems or acoustic spaces from a number of measurement positions. Because the analyzer's unique Delay Finder function locks in on and compensates for the propagation delay between speaker and microphone in less than a second, it is extremely easy to reposition the microphone and make measurements from another position in the space.

Is it really necessary to use SIM on a continual basis? Couldn't I just EQ the system once, lock off the equalizers and forget about it?

It is possible to do so, of course. Unfortunately however, experience has been that while the practice yields substantial initial benefits, it does not necessarily ensure consistent system performance in the long term. First of all, in complex sound systems, a number of unpredictable factors may come into play over time. Aging or stressed components can change their characteristics. Replacement of aged or blown speakers can result in broadband variations of component levels. Acoustic changes by moving equipment or furniture around the room will also affect the tuning.

As time goes by, such factors can compound to degrade the sound quality. The only way to ensure that a system remains at peak performance is to provide a means to monitor it on an ongoing basis. SIM's memory storage allows tracking of the sound system to check for degradation.

Can SIM fix every acoustical or sound system problem?

Actually, SIM doesn't "fix" anything. SIM 3 System is a tool for acoustical analysis: it provides a clear, detailed picture of a sound system's performance in a space and can rapidly identify acoustic anomalies.

SIM 3 System can also facilitate system equalization - and my experience is that, given a well-designed and well-behaved sound system, complementary parametric equalization can fine tune a system with spectacular results.

If the sound system's characteristics change substantially at different operating levels, however, equalization will be ineffective. It is also important to remember that equalization is only effective in controlling problems that can be equalized. A loudspeaker with appreciable distortion, for example, may appear to have excessive high-frequency response. Equalization won't help this: rather, the distortion must be eliminated. Additional loudspeaker characteristics that must be controlled by other means include consistent response with varying signal level and linear phase response.

Nor can equalization "cure" bad sound design: destructive interaction between loudspeakers, for example, can't be equalized effectively, since its effects vary with position. Similarly, gain structure needs to be rationalized, polarity made consistent and sources of hum or noise eliminated before equalization can yield any appreciable benefits.

Does SIM 3 System perform automated equalization?

No, SIM 3 System only gathers and displays data about the sound system. How that data is acted upon is for the operator to decide.

After eight years of research, Meyer Sound has concluded that totally automated equalization is neither practical not necessarily desirable. Any program that seeks to automate equalization decisions must take into account a bewildering array of factors and act on the data unambiguously. The human brain is well equipped to integrate small anomalies in a frequency response curve, identify phenomena such as cancellations that should not be equalized, and arrive at decisions; computers do such things relatively poorly.

What if I don't want my sound system to be flat? I have a very specific house curve that I prefer.

No problem. SIM 3 System will assure that you get your preferred house curve more accurately and consistently every time.

Get more info about SIM 3:
Additional information and downloads are available on the Meyer Sound site.