This page features several MP3 files with various tones and sweeps. These files can be used for testing purposes of all kinds, for instance for testing audio equipment, or even tuning instruments.
The MP3 files are packaged inside ZIP files, not just to make the download smaller but to avoid all kinds of problems with people streaming these files directly from my site. Just unzip the files with your favourite utility and play them in a media player of your choice!
Warning: some of these files contain continuous high-pitched sounds which may cause damage to ears and speaker systems when played too loud! The author of this page is not responsible for any damage caused by incorrect use of these sounds.
These are 5 seconds each of two plain standard frequency tones: 440Hz (standard "A" note frequency) and 1000Hz (often used to measure RMS voltage). They can be used to tune instruments, test the output voltage of audio equipment, or whatsoever. To reduce transient effects, the tones have a 5msec fade-in and -out.
These are sine waves starting at 16Hz and increasing in frequency to 20kHz(*). This is the frequency range that a true "hi-fi" system should be able to reproduce. It's also the frequency range a human younger than 20 years with healthy ears should be able to hear (after that age, sensitivity to high frequencies decreases pretty much inevitably). Mind that most consumer audio equipment, like PC speakers, won't be able to reproduce anything below 50Hz or above 16kHz, or worse. If you want to test your ears, you should use high-quality headphones, and a high-quality sound card. It is possible that low-quality equipment will produce audible distortion on the highest frequencies, giving you the false impression that you can hear them after all.
The sweeps come in 2 varieties: linear and exponential. The linear sweep's frequency ramps up linearly, meaning that after a time t, the frequency is f1+t*(f2-f1)/ttot, where f1 and f2 are the start & end frequencies respectively and ttot is the duration of the sweep. The exponential sweep follows an exponential curve: f1*exp(ln(f2/f1)*t/ttot).
The exponential sweep is the most "natural" sounding one, because the frequency response of our ears is logarithmic. In this sweep, there is always the same amount of time between the doubling of the frequency, i.e. between two octaves. The linear sweep, on the other hand, has the advantage that it's easier to determine which frequency is playing at a certain moment.
These sweeps have a 1/f power spectrum, corresponding to the power spectrum of pink noise, or the average power spectrum of natural sounds. This means that the instantaneous power of the sound wave is constant, and the total power in each octave is the same. Beware: the power in the electrical signal does decrease according to 1/f, because the amplitude of the wave decreases at 1/√f. The reason why this keeps the power of the sound wave constant is that the power of a sound wave is proportional to its frequency squared.
These files can be used to test audio equipment (detect resonance or absorption peaks), audio codecs, or to test audio spectrum-based equipment for its responsiveness. When playing these sweeps, ideally you should not hear sudden increases or drops in volume. For a speaker setup these will be pretty much inevitable due to standing waves in the room, but they can be reduced with proper equalizing and sound-absorbing materials.
(*: due to limitations of the LAME encoder that I used to create these MP3 files, some of the sweeps have a small drop-out at the end, starting at about 19kHz. These files are marked with an asterisk.)
Each sweep comes in a 5 second and a 10 sec. version. Additionally, a 10 sec. exponential sweep which only goes up to 1600Hz is available. This sweep is especially suitable for testing (sub)woofers.
These are the same sweeps as above, except they have a constant amplitude. BEWARE: this means that the power of the sound wave increases with the square of the frequency, even though the power of the electrical signal remains constant! In practice this means you can damage your ears by playing these files too loud. Also, if you would play these sweeps on 50W RMS multi-way speakers, for instance, at such a volume that they start out at 50W RMS, the tweeters risk burning out. The reason is that multi-way speaker setups are designed with the typical 1/f power spectrum in mind, meaning that the tweeters will have a smaller absolute power rating than the woofers. It would be useless to design the tweeters to handle the same amplitude sine wave as the woofers, because this should never happen. It will only happen if music is played so loud that the amplifier clips excessively, causing a compression of the sound which pushes the high-frequency content beyond the typical 1/f distribution. And that's why tweeters often burn out first in abused speaker systems. The 1/f power spectrum is also one of the reasons behind the 10dB boost for the LFE channel in 5.1 surround systems.
For most people these sweeps are useless, you should use the 1/f sweeps instead. Only download and use these sweeps if you know what you're doing.