AP - The Recognized Standard In Audio Test

Generating Low Frequency Triangle Waves with SYS-2722

Created 16 Sep 2009

Question

How can I generate a triangle wave with a frequency of 1 Hz at the digital output of a SYS-2722? I want to use the signal to test for suppression of pop noise in an amplifier.

Answer

You can generate a triangle wave by selecting Arbitrary Waveform in the waveform selection box of the Digital Generator. You will need to create the waveform in a third party application, save it as a .wav file, and then import it into the Digital Generator in AP2700.

Note that the buffer size of the SYS-2722 is 16 kSamples (16,384 samples). Therefore, to generate a 1 Hz waveform, the sampling frequency must be limited to 16.384 kHz. If you want a more conventional sample rate like 48 kHz, the frequency of the triangle wave would have to be higher. For example, with a 48 kHz sample rate, the buffer length is 16,384/48,000, or 0.3413 seconds. As a result, the lowest frequency that can be generated is 1/(0.3413 seconds), or 2.926875 Hz.

Note that it is important to have an integer number of cycles fit exactly into the buffer, to avoid discontinuities in the generated signal. This is because the generator wraps around to the beginning of the buffer when it reaches the end. The above two combinations of sample rate and waveform frequency will ensure that exactly one cycle of the waveform fits into the buffer.

There are many third party applications that can be used to create the .wav file containing the triangle wave. Matlab and LabVIEW have this capability, and there are also inexpensive programs available on the web on a try-before-you-buy basis.

The related Low Frequency Triangle Wave download contains the two waveforms discussed above. Both are 24-bit with 16,384 samples and contain one cycle of a triangle wave. One has a frequency of 1.0 Hz and is sampled at 16.384 kHz. The other has a frequency of 2.926875 Hz and is sampled at 48 kHz.

Once the .wav file is created, you can import it into the Digital Generator of the SYS-2722 as shown in the figures below.

Figure 1  Importing an arbitrary waveform into the digital generator.

 

Figure 2  The waveform import dialog box.

 

Figure 3  Viewing the digital output by looping it back into the digital analyzer (GenMon).

Note that such a low frequency waveform can not be generated in the analog generator of the SYS-2722, because it is transformer coupled. The lowest frequency that can be generated using the analog generator is approximately 10 Hz.

*****
jb

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