Basic ETF5.0 Demo Package

ETF runs in all 32 bit Windows operating systems. ETF is a post processing application and computer size/speed is irrelevant to its operation. To ensure efficient operation, a user should have 64 MB of memory and 400 MHz of processing speed. This and a stereo full duplex (play and rec simultaneously) sound card are the hardware requirements for the software. Almost all low cost PC based sound cards fit this requirement. The demo download contains almost all of the functionality of the program but with no performance enhancement package functionality. You cannot save files but can take all measurements with no time limit on functionality.

ETF was designed for room acoustics and small medium sized rooms. It is ideally suited to home theater installations and where high quality playback is required.

The basic ETF package includes all of the capabilities of conventional acoustic analyzers. The basic package includes impulse response, unfiltered frequency response, 1/2,...,1/12 fractional octave measurements, 1/3 Oct RT/60, 3D graphical representations of spectral decay, band filtered energy time curves, microphone speaker distance (automatic) and phase measurements. All measurements are gated meaning that room reflections can be removed from the measurements and pseudo anechoic measurements can be taken.

The demo download software can be tested for correct operation with a computer and sound card for precision and accuracy as well as be used to take actual measurements. The demo contains a recommended test for all new users to ensure that data is taken correctly & reliably. This is outlined in Help->Getting Started. ETF has a new beta mixer and should simplify the sound card mixer settings on most sound cards.

The performance enhancement package should only be considered by those who need to use the analyzer for EQ adjustment, distortion measurement or precise measurement of low frequency room acoustics involving individual room modes. ETF provides very convenient ways of comparing measurements as well as the capability to obtain practical & useful low frequency room acoustic measurements that are less corrupted by background noise than with most analyzers.

The Radio Shack SPL meter combines a microphone and a preamp (line level) that can be used to drive the input of a sound card at the line input (not the mic input). This is a perfectly good choice for a microphone to tune low frequency acoustics and see room reflections at higher frequencies. If this is the intended purpose of the software, then the low cost RS meter is all that should be used. A calibration file link for this unit resides on our site on the support page. This file makes the microphone roughly accurate to a dB up to about 5 KHz.

If the purpose of the software includes equalization at mid & high frequencies, a calibrated microphone is recommended. The calibrated microphone & preamp on our site costs $250.00 USD, including delivery almost anywhere in the world. Its specifications are posted on the web site.

The input of the sound card must be stereo and standard "line level" input. The mic level input is not used with ETF software. The output must also be stereo and standard "line level". The card must be able to both play and record at the same time (full duplex operation). Most low cost sound cards for desk top PC's provide these necessary capabilities.

There is no advantage to using an expensive sound card with ETF software. Natural acoustic noise is much louder than even the most noisy sound cards. Acoustic measurements typically have a dynamic range of 30 dB - 40 dB. Sound cards with 16 bits of resolution have dynamic ranges of 90 dB. This means sound card noise is completely washed out by up to 40 dB more acoustic background noise and the number of bits of resolution in the sound card becomes irrelevant. It is pointless to use anything greater than about 12 bits for acoustic measurements.

ETF uses a stereo sound card to obtain a single frequency response. The right channel supplies the signal to the system as well as recieves input from the microphone. The left channel sound card output is connected directly to the sound card input allowing ETF to subtract sound card response frequency errors from the measurement in the right channel. Sound card frequency response is unimportant because it is accounted for in the software.

The remaining parameter that describes sound card audio performance is distortion. Distortion is at an acceptably low level with most low cost PC based sound cards so that it is always irrelevant because loudpeaker non linearities are always much greater. Sound cards are well tested and compared at www.PCAVtech.com.

The Creative SoundBlaster MP3 USB card is the recommended sound card for cost (<60.00 USD) and flexibility (USB).

We recommend using optimum sub woofer placement using the methods illustrated in Demo Room on our web site followed by subsequent corrective electronic equalization. The results obtained using an electronic corrective device are usually better and cheaper when compared to passive devices at low frequencies. High frequency control of particular reflections is best accomplished using absorbers first with subsequent equalization. Although ETF provides the capabilities of making passive low frequency devices using a simple calculator and test procedure, the use of passive devices to control low frequency room acoustics is usually not recommended. Products from companies such as Behringer & Tag McClaren make electronic correction the ideal method of low frequency room control after the optimum subwoofer placement tests have been done with the software.

The best results in terms of distortion and response can normally be obtained by putting a subwoofer in a corner and controlling over excited modes with parametric equalization. This approach leads to an increase in efficiency by exciting all room modes. Not all rooms are well represented by this simple approach and various subwoofer locations should be tested to obtain the benefit of distortion reduction that is a result of efficient sub woofer placement. Ideal placement and electronic equalization can both flatten response and reduce distortion. The psycoacoustic response (see Performance Enhancement Package) can then be adjusted using low Q parametric controls.

The performance enhancement package is a set of capabilities that extend the standard analyzer capability in terms of analyzing low frequency room acoustics, EQ setting & Distortion measurement but is an added cost to the standard package.

All three enhancement licenses can be bought for $150.00 USD, or any one of three can be bought for $75.00 USD. This is available only to owners of a basic license.

Individual room modes can easily be resolved using the PSD / Sweep type measurement when conventional methods such as exponential sweeps and MLS fail at low frequencies due to excessive acoustic background noise. This method has a greatly improved low frequency signal to noise ratio over standard methods such as standard sweeps & MLS found on typical MLS, Pink & Sweep based analyzers. This high signal to noise ratio provides high resolution frequency measurements required to identify individual room modes that comprise the room + speaker response. This feature is important for diagnosing very low frequency modal problems. In most cases, the PSD sweep provides the resolution necessary to easily and clearly obtain 0.75 Hz in resolution for low frequency modal identification. It also provides the s/n ratio necessary to drive loudspeakers at very low SPL levels and obtain useful results.

This feature is beneficial to those with a need for accurate very low frequency measurements. This method works well for "stationary" noise such as cyclic machine noise, traffic, electrical hum and large air exchange systems. It doesn't work well for transient noises such as door slams, conversations, or music. The PSD sweep is subjectively much more quiet than conventional signals due to the fact that the signal puts most of its energy where background noise exists in the spectrum.

This is fully explained with many example measurements in the help files contained in the demo download under Performance Enhancement Upgrades.

Human hearing does not work the same way as a simple spectrum analyzer. To this end, ETF provides a psychological response that calculates frequency response in a way that more closely approximates human hearing.

The ETF Psycoacoustic response differs from standard 1/3 octave analyzers in the way it processes results. The standard method takes approximately 200 ms of data, finds the frequency response and smoothes that curve to get a 1/3 octave response.

The method used in the psychological response is to truncate time data using gates (frequency dependent) and therefore obtain a 1/3 octave response by gradually excluding later reflected data from the measurement as frequency increases instead of averaging it in.

This is fully explained with example measurements in the help files contained in the demo download under Performance Enhancement Upgrades.

The measurement of distortion in domestic living situations has always been difficult for two reasons: (1) Noise, (2) Interfering Room Acoustics. Conventional two tone or single tone measurements do not give "musical" insight to the amount of distortion that is actually present.

The ETF multi tone distortion measurement provides 16 computer optimized frequencies to produce over 600 harmonics and IM components that can be measured for second and third order distortion artifacts that are characteristic of loudspeakers operating within normal limits.

This is a much more realistic approximation than a two tone measurement to actual real world music. The 16 excitation frequencies for this test are B weighted in level across the full frequency range.

ETF provides a statistical test to show if measurements are valid in the presence of background noise.

This is fully explained with example measurements in the help files contained in the demo download under Performance Enhancement Upgrades.