A collection of useful sound files for audio test purposes has been posted on webpage www.dogstar.dantimax.dk/testwavs by Fred Nachbaur. These files, except where noted, are in standard Windows '.wav' format (but are zipped). Short descriptive text items are included within the wav files, should one have a wav player/editor capable of reading them (eg, CoolEdit).
Most of the samples on the site are 10 seconds long, but can be concatenated if needed since all are set to begin and end at the zero-crossing point. Where applicable, the zip files also contain a .png image of the spectrograph or spectrogram of the corresponding wav file. Fred Nachbaur provides the following descriptions.
Noise files
* white.zip: this is 'white noise,' with a frequency distribution of 1 (ie, all components of equal intensity). On a spectrograph, this corresponds to a 'flat' response.
* pink.zip: this is '1/f noise,' with a frequency distribution of 1/f, or a 3 dB per octave roll-off. It is generally considered the kind of noise most prevalent in nature.
* brown.zip: deriving its name from 'Brownian motion' - the kind of noise associated with such 'random walks.' It has a frequency distribution of 1/(f2), which is to say, a roll-off of 6 dB per octave.
* blue.zip: this is, in a sense, the inverse of 'pink' noise, with a frequency increase of 3 dB per octave. Intensity is proportional to f.
* violet.zip: and this is the inverse of 'brown' noise, with a frequency pre-emphasis of 6 dB per octave, or an intensity characteristic of f2.
Sine sweeps
* sweeplin.zip: this starts with one second of 20 Hz, followed by a fast 'sync pulse' which might conceivably be useful for synchronising a storage oscilloscope. Immediately thereafter, it sweeps linearly from 20 Hz to 20 kHz at a level of
-3 dB (relative to 0 dB = 100% modulation). Total duration of the sweep is 10 seconds.
* 3stepoct.zip: this file would be more useful for manual frequency response measurement. Unlike the other files, this is in MP3 format; it is suggested to convert it to a wav file first. It has 2 s samples of fixed tones from 20 Hz to 20 480 Hz, spaced logarithmically in 1/3 octave increments, for a total of 31 samples. The actual frequencies are included in the ID3 tag of the MP3 file itself. They are also shown in the .png spectrogram.
Square waves and bursts
* square.zip: this contains square waves at four different frequencies: 10 Hz, 100 Hz, 1 kHz, and 7,35 kHz (the 7,35 kHz rate was chosen to avoid artifacts due to digital aliasing.)
* bursts.zip: this file contains three separate files containing tone bursts. These would be useful for checking amplifier transient response. All have a repetition rate of 10 bursts per second, so it would be useful to set up an oscilloscope for a horizontal scan rate of 5 Hz.
Intermodulation tests
* imd_smpte.zip: this contains 10 s of 60 Hz at -3 dB, superimposed on 7000 Hz at -12 dB, in compliance with the SMPTE/DIN standard for intermodulation distortion measurement for audio equipment. If you do not have a way of getting a spectrograph of your amplifier's response, this still might be useful in an auditory test; both tones should be pure and clean, with no warbling or 'edginess' to them, and no additional audible artifacts. Played at different volume levels, you will readily hear if your system has excessive IMD especially at high volume; the low note will become progressively brassier, and the high tone will begin to warble as IMD increases.
* imd_7350.zip: essentially the same idea, except that the high tone is 7350 Hz (an even sub-multiple of the 44 100 Hz sample rate) to prevent the possibility of aliasing artifacts affecting measurements. See www.dogstar.dantimax.dk
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