Created on 2010-12-23 20:06:00
Question:
I have a special purpose waveform, which I want to use as a signal source for a test, saved as a .wav file. How do I play a .wav file out of the analog or digital generator on a 2700 Series instrument?
Answer:
The Analog or Digital generator can play arbitrary waveforms in the Audio Precision .agm or .ags (mono or stereo) waveform format. To play a .wav file, you use the File > Import > WAV File command to import, convert, and load the waveform into the generator waveform buffer all in one step.
1) On the Analog or Digital Generator Panel, select Arb Wfm (arbitrary waveform) in the Wfm select box.
2) Select File > Import > WAV File.
3) Browse to the desired .wav file and click Open. Note that this import utility works best when the .wav file is located on a local drive (not on a network drive).
4) In the Import MS (.wav) Waveform window, select the Analog or Digital Generator. Here you can also change channel assignment, or truncate the beginning of the waveform.
5) Click OK. This will convert the waveform to the .ags or .agm format and load it into the Generator.
Note that the Amplitude control on the Analog and Digital Generator panels determines the level of a full-scale waveform signal. For example, if a waveform contains a tone at -20 dB, and the Amplitude is set at 0 dBu, then the actual output level of the tone will be -20 dBu.
The arbitrary waveform generator buffer is limited to 16,384 (16 k) samples. If a longer .wav file is loaded, the waveform is simply truncated. When the 2700 Series instrument generates the waveform and reaches the end of the buffer, it will wraps around to the beginning. Therefore, to avoid glitches in the signal, you need to ensure that the signal is synchronous with the 16 k buffer. You can find the nearest synchronous frequency (fsync) of a sine wave at a nominal frequency (fnom) using the following equation, where LBUFF is the buffer length in samples, SR is the sample rate in Hz, and Integer denotes rounding the number to the nearest integer:
For example, if you wanted to generate a 1 kHz sine wave, the nearest frequency that is synchronous with the 16k waveform buffer is fsync = 999.0234376 Hz, with exactly 341 cycles in the 16 k sample buffer.
If you need to generate a signal from a .wav file that is larger than 16 k samples, you can use the Special Pass Thru mode to connect a digital signal source (such as the output of a soundcard).
Note that Audio Precision’s line of APx500 series audio analyzers have a much larger generator buffer size of 32 M samples (which is divided by the number of channels being generated). This corresponds to a buffer length of almost 6 minutes for a stereo signal at a 48 kHz sample rate.
Applies to: AP2700, ATS
