Generally we’ve used Sony cameras in the field for digital ATV, with an HDMI cable running from the camera to the TV modulator.
Last year I got a small, inexpensive CX405 model. I recently tried using it for the Boulder-area weekly ATV net, and no one could hear me. A little digging with the DVB-T test tool revealed that the audio stream was simply absent — no sound was being transmitted at all.
It turns out that newer Sony cameras don’t put out any audio through the HDMI cable (except during playback from a recording). Sony says (as of 2015), “There are no Sony Handycam models that can pass the audio through while recording the video. Again, both video and audio passthrough is only possible when the camera is on playback mode [actually, the issue wasn’t recording, but just live output out the HDMI jack, recording or not].”
This has not been an issue for older models such as the Sony CX430V and AX33.
Also note that the behavior of the Hi-Des modulators is to omit the audio elementary stream from the output transport stream (TS) when no audio is present on the HDMI input. The PID is still listed in the PMT, so the test tool can easily identify it as missing.