{"id":32190,"date":"2026-03-09T12:55:27","date_gmt":"2026-03-09T19:55:27","guid":{"rendered":"https:\/\/digilent.com\/blog\/?p=32190"},"modified":"2026-04-15T09:56:02","modified_gmt":"2026-04-15T16:56:02","slug":"why-your-triggered-capture-doesnt-start-at-sample-0-from-the-forum","status":"publish","type":"post","link":"https:\/\/digilent.com\/blog\/why-your-triggered-capture-doesnt-start-at-sample-0-from-the-forum\/","title":{"rendered":"Why Your Triggered Capture Doesn\u2019t Start at Sample 0: From the Forum"},"content":{"rendered":"

The Question<\/h4>\n
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A user getting started with the Analog Discovery 3 (AD3)<\/strong> wanted to generate a waveform using the Arbitrary Waveform Generator while simultaneously sampling an analog input – both synchronized in time using a software trigger.<\/p>\n

While the triggers appeared coincident when viewed on an external oscilloscope, the captured analog input data told a different story. The waveform didn\u2019t appear at the start of the sample buffer. Instead, it showed up roughly halfway through a 12,500\u2011sample acquisition.<\/p>\n

With both Analog Out and Analog In configured for software triggering, the user couldn\u2019t find anything in the WaveForms SDK or reference documentation explaining this behavior.<\/p>\n

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The Answer<\/h4>\n

The key detail comes down to how trigger position is defined for Analog In acquisitions when using the WaveForms SDK.<\/p>\n

Unlike what many users expect from a programming perspective, a trigger position of 0.0<\/code> does not place the trigger at the beginning of the data buffer. Instead, the trigger position is defined relative to the center of the acquisition buffer, similar to how a traditional oscilloscope works.<\/p>\n

That means:<\/p>\n