Problems reading XLR Analog Audio In with IDeckLinkInput

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Jules Davis

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Problems reading XLR Analog Audio In with IDeckLinkInput

PostWed Apr 12, 2017 9:38 am

I am using a Blackmagic DeckLink 4K Extreme Capture card to capture video from a mini 4k camera via the Blackmagic SDK with the IDeckLinkInput interface.

This works fine when the audio is coming directly from the camera, however I have a requirement to support audio connection from an analog source via the XLR connector.

I can use the configuration tool to reconfigure the device to get audio from the XLR port, plug in an analog microphone and then monitor it in Media Express and see the audio levels.

However, when I use the IDeckLinkInput interface to capture the video/audio I get strange results.

The samples read from IDeckLinkAudioInputPacket->GetBytes() in the VideoInputFrameArrived callback appear to be at least 1000x to small / low and very noisy. (As compared to when reading audio with the same code from the camera via SDI input).

I have set the interface to 32 bit audio samples and expecting the samples to be in the range int-min to int-max.

How do I read from the XLR reliably?

Jules Davis
CTO Focal Point VR Ltd

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