Chrome Version       : 71.0.3569.0 (Official Build) canary (64-bit)
OS Version: OS X 10.13
URLs (if applicable) : https://codepen.io/anon/pen/qJrQZq?editors=1010
Other browsers tested:
  Add OK or FAIL after other browsers where you have tested this issue:
     Safari:
    Firefox: OK
    IE/Edge:

What steps will reproduce the problem?
1. Create an <audio> element where id="sound" and loop="true"
2. Add the following JavaScript:

```
const mediaElement = document.getElementById('sound');

const startPlaying = () => {
  const context = new AudioContext();
  const source = new MediaElementAudioSourceNode(context, { mediaElement });
  
  const panner = new PannerNode(context);
  panner.panningModel = 'HRTF';

  panner.positionY.setValueAtTime(2, context.currentTime + 2);
  panner.positionY.setValueAtTime(-2, context.currentTime + 4);
  panner.positionY.setValueAtTime(0, context.currentTime + 6);
  
  panner.positionZ.setValueAtTime(1, context.currentTime + 8);

  panner.positionY.setValueAtTime(2, context.currentTime + 10);
  panner.positionY.setValueAtTime(-2, context.currentTime + 12);
  panner.positionY.setValueAtTime(0, context.currentTime + 14);

  source.connect(panner)
     .connect(context.destination);
}

mediaElement.play().then(startPlaying);
```


What is the expected result?

For the first 8 seconds, your listener should be positioned at 0,0,0 and your sound should be panned up, then down, then back to the centre.

The same should repeat in the next 8 seconds, with a slight timbral/volume change because your sound is now further from you in the Z direction.


What happens instead of that?

In the first 8 seconds, the sound is actually panned to the *right*, then further right, then back to the centre.

After setting positionZ to 1 (at T+8 seconds), the sound doesn't pan to the right anymore, and pans up, down and back to the centre as expected.


Please provide any additional information below. Attach a screenshot if
possible.

It seems like the HRTF functions don't work as expected when both the listener and the panner are at the same positionZ – this applies also when both are at positionZ=1.

This might be a problem for applications where only positionY should change, for whatever reason, as it then introduces unintended horizontal panning.