 |
|
|
| ||||||||||||||||
| ||||||||||||||||
|
What is SIM System II?
As every experienced concert sound engineer will attest, equalizing a reinforcement loudspeaker system in an empty hall does not assure consistent, dependable sound in a performance. As soon as the hall fills with people, its reverberant qualities change - sometimes radically - and this affects the sound system's response. As the concert proceeds, increasing air temperature and humidity caused by the crowd aggravates the problem. SIM System II is designed to address this problem by making it possible to measure and equalize a sound system unobtrusively, during a concert, with an audience present.
SIM System II 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 System II 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 2201 Analyzer's internal hard drive for post-processing. Separate display "pages" permit analysis of the transfer functon (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 performance space in suitable positions and connected to the SIM 2201 Sound Analyzer through multiple SIM 2403 Interfaces. 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 2201 Analyzer as the measurement reference.
Pre-concert equalization is then performed using either the analyzer's noise source or pre-recorded music as the test signal. Room resonances, loudspeaker response aberrations, echoes and other sonic perturbations can be identified and corrected by adjusting the system equalizers. Subsystem levels can be balanced and fill system delays set quickly and accurately.
In concert, the SIM System operator makes multiple measurements throughout the performance, switching among the microphones by computer control from the SIM 2201 Analyzer and adjusting the system equalization as necessary.
What are the advantages of SIM System II over conventional FFT analyzers?
Accuracy - The SIM 2201 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 2201 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 2201 is over ten times faster at data acquisition, display and storage than competing units such as the BrÜel & Kjaer models 2032/2034 or Hewlett-Packard models 3582A/35660A Spectrum Analyzers.
Power - To achieve performance equivalent to SIM System II 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 equalled by twenty-seven 3582A Analyzers in parallel.
Efficiency - SIM System II 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.
Ease of Use - SIM System II is extremely compact and lightweight. Its command structures are optimized for acoustical measurment tasks, with elements labeled using standard audio terminology, making the instrument very ease to learn and operate. Integrated procedures automatically set the instrument configuration for a wide variety of sound system testing and alignment tasks.
What is the difference between the three hardware/software versions of SIM System II?
SIM System II is currently available in three versions: v. 2.0 Lab, v. 2.3 Stereo and v. 2.3 Multi-Channel. Each version is designed for distinct applications.
v. 2.0 Lab - SIM System II v. 2.0 comprises the SIM-2201 Sound Analyzer with single DSP engine, and system software v. 2.0. Optimized for laboratory operation and automated measurements of two-channel systems, v. 2.0 is upwardly expandable to v. 2.3s or 2.3m.
v. 2.3 Stereo - In this version, the SIM 2201 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 dual-channel sound reinforcement systems and recording studio control room monitors.
In situations where there are not time constraints, the SIM 2201'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.
Equalization changes may then be made on the basis of memory traces. For this reason, v. 2.0 is an ideal tool for acoustical consultants as well as for those sound reinforcement professionals who deal mostly with two-channel systems.
v. 2.3 Multi-Channel - This version incorporates three DSP engines in the SIM 2201 Analyzer, along with provisions to address as many as eight SIM 2403 Interface Networks. v.2.3 is designed for working with complex, large-scale sound systems and performing live, multiple-point measurements during a performance.
This version is optimized for speed, and its functional design is the result of Meyer Sound's eight years of experience working with large-scale concert systems and complex theatrical sound systems. For sound reinforcement professionals whose primary activities employ such systems, v. 2.3 is the tool of choice.
Is it really necessary to use SIM at every performance? Couldn't I just rent a machine, EQ the system during one representative performance, lock off the equalizers and send the machine back?
It is possible to do so, of course. In the early years of SIM, before the elegant and compact SIM System II was available, SIM was normally used in this manner.
Unfortunately however, our experience was that while the practice yields substantial initial benefits, it does not necessarily ensure consistent sound system performance in the long term. First of all, varying audience attendance levels, air temperature and humidity conditions can substantially alter a hall's acoustics and thereby change the perceived sound quality. Moreover, in complex sound systems, a number of unpredictable factors may come into play over time. Aging or stressed components can change their characteristics. Shows with numerous complex set changes can present different acoustical conditions on different nights. Delay lines may slip or become accidentally misadjusted.
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. Anything less is like flying a plane without instruments: you might get away with it on clear days, but you'll be in trouble at the first sign of inclement weather.
This is one reason why SIM is no longer an expensive, custom service. With the advent of SIM System II, it is possible for sound reinforcement professionals to own a measurement system that gives reliable, accuratedata in concert, every night - so they can be sure that their PA is always working at peak performance.
Can SIM fix every acoustical or sound system problem?
Actually, SIM doesn't "fix" anything. SIM System II 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 anomalies. Whether, and how, those anomalies are corrected is another matter.
SIM System II is designed, in part, to facilitate system equalization - and our experience is that, given a well-designed and well-behaved sound system, complementary parametric equalization can effectively compensate for many acoustical anomalies. If the sound system's characteristics change substantially at different operating levels, however, equalization will be ineffective.
Moreover, there are practical limits to electronic solutions for acoustical problems. Often, it is much more effective to employ acoustical means such as adding absorptive or reflective materials. The data gathered by SIM can guide such choices.
Is SIM for use only with Meyer sound systems?
No, SIM System II is a general-purpose acoustical analyzer. While we obviously prefer that people use our loudspeakers, that is not a prerequisite.
It is important to remember, however, 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 System II perform automated equalization?
No, SIM System II 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, we have concluded that totally automated equalization is neither practical not necessarily desireable. 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 System II will assure that you get your preferred house curve more accurately and consistently in every venue. Moreover, it will assure that the curve is the same in all areas of the house - so every audience member hears the same balance that you do at the mix position.
Are there any other reasons why I should have SIM System II?
SIM System II is unique in its field. No other acoustical measurement tools address the problem of using an unpredictable excitation signal like music, which is neither truly random nor entirely periodic. SIM System II addresses real-world problems with advanced technology and user-friendly controls. It is alone among acoustical analyzers in this regard.
|
|
Contact
Us | Terms of Use | Trademarks |
