The most common question we get is "How do I use the test tones?"

In order to use the test tones most effectively I recommend a spectrum analyzer and a flat microphone to display the results. A spectrum analyzer will display the audio power in a particular frequency range. A 'Flat Microphone' is a microphone that preserves the frequencies of the original sound as much as possible. Most users do not have access to a spectrum analyzer or a flat mic so testaudio.com is now offering a cheap way out - a software bar type spectrum analyzer to use with your own computer and sound card ( Windows only ).

The spectrum analyzer software and tones are available for download by testaudio.com members. Sign up today for all this great stuff!

A little background....

Historically all spectrum analyzers were analog in nature - subject to electronic component tolerances, heat, changes in component value, etc. This meant that the analyzer had to be 'calibrated' on a regular basis for critical applications. In the digital age things are a little different. Sure the hardware is still analog for data acquisition ( the microphone, preamp, and A/D (analog to digital) converter) but the actual frequency analysis is done entirely in the digital domain using software based on calculus - specifically an FFT ( Fast Fourier Transform). This technique leads to the formation of 'BINS' ( similar to center frequencies in traditional band pass filters like those found on graphic equalizers ). Any digital analyzer using an FFT will have BIN frequencies that are not always on common frequency centers. Instead of 1k hz the BIN  frequency may be 1001.29 hz.

Although analog filters, like those on your equalizer, are often off +/- some percentage in the analog world this difference is subject to shift over time due to component changes caused by age, heat, temperature, etc. so your 1khz equalizer slider may actually be a 980 hz slider or a 1020 hz slider. Next year it could be 1030 hz. In the digital world this is fixed and can't change. If our BIN frequency is 1001.29 hz it will be 1001.29 hz tomorrow, next year, and 10 years from now.

What this all means is that I can now produce an audio file of fixed frequency that will match the BIN frequency and allow an accurate centering of frequency to display. Using an analog analyzer might result in inaccurate readings due to the filter bandwidth if the source tone was not on center with the analyzer filter.

The Spectrum Analyzer Software

There are no user adjustments - just a simple display. The GREEN bar on the left represents the total signal power. The orange bars represent the power of a particular frequency ( indicated below the display ). The DB levels are indicated on the right hand side.

Step 1: Connect your sound source to your sound card.

If using a microphone attach it to your computer sound card's microphone input. Other sources such as mixing board outputs can be used but be aware that every element in the chain alters the response so the less the better. The standard application is just a microphone directly into the sound card. That way only the mic and sound card will affect the results. If the mic and sound card are reasonably flat ( most sound cards today are reasonable ) then you'll get decent results.

Make SURE you place the mic at a distance from your computer as the fan noise will become a problem with a mic placed too close. See the image below.

Step 2: Start the Spectrum Analyzer Software

To use the software just double click the file you downloaded. The display will appear but may or may not display anything based on the input to your sound card.

This software is designed to allow maximized full screen display for viewing at a distance as in many cases you'll be placing the mic and analyzer away from the adjustment controls.

Step 3: Set Windows Recording Input

To get a reading you must set your Windows PC for the correct recording input - the software only takes input from your sound card.

Click this icon usually found in the lower right hand corner of your screen. If it's not there you may need to ask someone for assistance accessing the  windows sound mixer.

Once the sound mixer is open click 'options' then 'properties'.

In the window you'll see the options below. Select 'Recording' then click 'OK'

Depending on the input your using check the 'select' box on that item and adjust the slider until you see a reading on the spectrum analyzer.

The image below shows an 'open microphone' placed near the PC. This is just picking up the fan noise. This is also typical of ventilation systems.

Step 4: ANALYZING

The objective is to have all orange bars ( except perhaps those above 16k and below 64hz ) at the same height - simple. This is done by playing the FFT BIN tones and adjusting your systems's equalizer , positioning your speakers, adding padding to the walls, etc. Usually the microphone is placed where you'll be listening.

You'll need to play the test tones at a volume which will overcome the room noise. In some rooms this may be excessive so be considerate of your neighbors as test tones can be the MOST annoyingly unpleasant sounds - particularly at 2 in the morning. You may have to turn off your air conditioner or heating system temporarily to remove this noise. DO NOT play the tones so loud that they might damage your hearing - there's no need to go any louder than standard listening levels.

Using the Analyzer adjusting your system is easy. You can start with the full spectrum file ( 01_FFT_BINS_COMPOSITE ) to get an overall picture. Note the GREEN BAR is higher than all the ORANGE BARS. This is because the green bar represents the sum of all audio power and the orange bars represent only a portion of the frequency spectrum composing the signal. The 01_FFT_BINS_COMPOSITE file contains all the BIN CENTERED frequency at the same level. Note the dropout below 43 hz and above 16khz. This is typical as most audio systems 'roll off' at these levels. NOTE: Do not overcompensate by boosting these frequencies as the results of the analyzer in these ranges if usually low due to sound card and cd player input and output filters, microphones, wire, etc. Focus on the frequencies from 100hz to 12khz for now until your comfortable with the adjustments.

Important!! - watch the GREEN BAR - Don't let it go above 0db. You should keep it down around -4db. If this clips ( rises above 0 ) then the entire reading will be incorrect as the wave will now contain additional frequencies caused by distortion.

Looking at the image below you'll see a BIN CENTERED 1001.29 hz -4dbfs sine wave being input into the testaudio.com spectrum analyzer. The GREEN BAR represents the total signal strength and the ORANGE BAR is the spectrum output of the 1001.29 hz wave.

PINK NOISE

The image below shows the spectrum analyzer with pink noise as the input through a cd player, mixer, and sound card. You'll note that the slope isn't perfect - this is part of what we're trying to compensate for with this tool. Pink noise should slope at -3db per octave. ( An octave is 2x the previous frequency meaning that if the level is -12db at 1khz then the 2khz should be -15db, 4khz should be -18db, etc. for PINK NOISE )

CLASSICAL MUSIC - a typical response with music playing into the analyzer. Note the GREEN bar is always higher than the ORANGE bars.

Have Fun!

Disclaimer:

The software spectrum analyzer is offered FREE to paid members of testaudio.com. No warranty of any kind is offered. The software is being offered 'as is' and users agree to use at their own risk. This is in accordance with our site terms.

The software works on all computers in our test environment but can't guarantee it will work on yours. If it does that's great - you've got a nice bonus. If it doesn't then please contact us with your operating system, sound card, microprocessor, motherboard, system configuration and the exact error you receive.