The equalizer test tracks, included in the Subwoofer Test Pattern Premium suite, include several sine waves of equal amplitude at specific frequencies. The frequencies of each sine wave are placed around standard equalizer frequency points. There are three sets of standard frequencies: the first set has 12 frequencies, the second 15, and the last one has 31. The frequencies are values spaced logarithmically and span representatively over the 20 Hz-20 KHz range. The tracks are 5 minutes in length and recorded at 0 dBFS. These are among the most important tests in the suite.
12 band eq test.wav (track 68 on audio CD) 15 band eq test.wav (track 69 on audio CD) 31 band eq test.wav (track 70 on audio CD)
The objective of these files is to help "flatten" your listening room: that is, using your equalizer settings to compensate for variations in sound caused by speakers, objects in the room, and so on. If a particular frequency range is too "hot" you can tone in down a bit; if it's too muted, you can increase that frequency range. Then you will be able to hear your music as it was meant to sound.
(Remember as you do this: there is no absolute right or wrong. The settings of your audio system should be tuned to your preferences. If you like a little more bass or midrange to highlight vocals, by all means adjust the equalization to match what you like.)
Start playing the EQ tracks with the 12-band test, then later move to the 15- and 31-band tests. This will let you adjust a simple equalizer or a complex one depending on the capabilities of your equipment: you can adjust the EQ settings in three stages, each stage corresponding to a specific standard, 12, 15, and 31 bands. In this way you can tune finer changes as you go from the simpler EQ setting to the complex 31-band one. This method can ease the flattening process.
The 12-band file has tones at the following frequencies: 25Hz, 32Hz, 40Hz, 64Hz, 125Hz, 250Hz, 500Hz, 1k, 2k, 4k, 8kHz, and 16kHz.
The 15-band file has tones at these frequencies: 25Hz, 40Hz, 63Hz, 100Hz, 160Hz, 250Hz, 400Hz, 630Hz, 1kHz, 1.6kHz, 2.5kHz, 4kHz, 6.3kHz, 10kHz, and 16kHz.
The 31-band file has tones at 20Hz, 25Hz, 31.5Hz, 40Hz, 50Hz, 63Hz, 80Hz, 100Hz, 125Hz, 160Hz, 200Hz, 250Hz, 315Hz, 400Hz, 500Hz, 630Hz, 800Hz, 1kHz, 1.25kHz, 1.6kHz, 2kHz, 2.5kHz, 3.15kHz, 4kHz, 5kHz, 6.3kHz, 8kHz, 10kHz, 12.5kHz, 16kHz, and 20kHz.
EQ band response for the 31-band standard. Each band has the same amplitude; however when measured the amplitudes are changed by the system and room response. These are the differences that need to be compensated or flattened using the equalizer.
You will need one or two microphones with flat response for this test: condenser microphones are recommended — they have flatter frequency responses than dynamic microphones. (You can use a microphone with different response but you will need to check the frequency response curve of your microphone. It is important to make an optimal EQ measurement because all the adjustments will depend upon it.) The microphone should be placed at the focal point of the room and should be connected to an analyzer or a computer running a graphic equalizer application. The free version of TrueRTA Audio Spectrum Analyzer will do the job nicely.
Alternatively, you can use a sound pressure meter such as Radio Shack's digital sound level meter.
Play the tracks at a single volume while using the microphone or sound level meter to identify which frequencies are amplified or attenuated.
As your audio system plays the EQ test files, the analyzer will show the amplification or attenuation of each band you are testing. Adjust the stereo's equalizer to compensate for the highs and lows to attain an ideal audio image.
Adjust your EQ until the response is totally flat. It is not always possible to reach a perfect flat room; however, cycling through the three stages can smooth the EQ settings to reach an optimum configuration.