Tech Tip:Free Test Equipment For Your Studio
Generate test tones and sweeps on the cheap
By Craig Anderton
Test tones are useful for everything from checking your studio's acoustics to finding out how a venue will affect your live sound. But who wants to go through the hassle of getting a bunch of test equipment and learning how to use it?
The good news is that you don't have to, because if you have a digital audio editor like Sony Sound Forge, Steinberg Wavelab, Adobe Audition, etc., you can create your own test tones - and sometimes frequency sweeps as well. These are very helpful not just to play back through your system, but to save as a file and load into samplers and other devices to evaluate how they perform. And of course, you can burn these to an audio CD if you want a test CD playable through any CD playback system.
CREATING A FREQUENCY SWEEP
I find a 20Hz - 20kHz sweep very helpful, so here's how to create one using Adobe Audition.
Go Generate » Tones (Process)
and choose the sample rate, channels, and bit resolution. Click on "OK."
- Under the "Initial Settings" tab, select a "Base Frequency" of 20Hz, "dB Volume" of 0 (assuming you want a "full code" signal), Sine for "Flavor," and under "Duration," enter the desired sweep length (15 seconds is a good choice). Under "Frequency Components," the 1 slider should be at max. All other fields should be set to 0 and all checkboxes should be unchecked (Fig. 1).
- Click on the Final Settings tab, then click on "Copy From Initial Settings."
- For "Base Frequency," enter 20000Hz. You don't need to change any other settings. The Final Settings screen should look like Fig. 2.
- Click on "Preview," and you'll hear the sweep.
- After you're satisfied that it works, click on "Stop," click on "OK" to actually generate the file, then save the file.
Here's how you'd generate a sweep tone in Sound Forge (Fig. 3). First, go File » New
and choose the sample rate, bit depth, and number of channels. Click on "OK," then go Tools » Synthesis » Simple.
With the Simple Synthesis window open, choose the waveform shape, length, start/end frequencies, etc. Clicking on "OK" writes the resulting waveform into the file you created initially.
Of course, you can also generate fixed frequency tones using a similar procedure; here's how to do it in Steinberg's Wavelab (Fig. 4).
Go Tools » Audio Signal Generator
and on the "Source" page, choose Sine, phase angle of 0, and the format (stereo or mono, bit resolution, etc.). Under the "Frequency" tab, set all Time values to 0, and the desired frequency with the "Median Freq. 2" parameter (set here to 440Hz). The other frequency parameters don't matter.
On the "Level" tab, set the tone's duration with the "Sustain Time" parameter. All other values can be left at the defaults.
Click on "Generate," and a window will open with the waveform. Save it, and your waveform is ready to go.
In the days of analog tape, common alignment tones were 100Hz, 1kHz, and 10kHz. But of course, using software lets you generate tones of any frequency. For your reference, standard 2/3 octave frequencies are 25Hz, 40Hz, 63Hz, 100Hz, 160Hz, 250Hz, 400Hz, 630Hz, 1kHz, 1.6kHz, 2.5kHz, 4kHz, 6.3kHz, 10kHz, and 16kHz. Standard 1/3 octave frequencies are 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.
As just one example of using test tones, try using them to hear how your room and other spaces respond; you just might be in for a few major surprises.