Nielsen’s enhanced encoding technology is being put through its paces in separate tests in two countries. The results are likely to determine how the measurement giant proceeds with encoding improvements planned for the U.S. in the fourth quarter.

Both Nielsen and Canadian ratings collective Numeris have emphasized the importance of capturing “valid” or “quality” listening—but neither has defined precisely what that means, at least not publicly. It’s an issue that Nielsen has said it will take up with its audio technical subcommittee as well the Media Rating Council and the NAB’s COLRAM (Committee on Local Radio Audience Measurement) group.

The different combinations of background noise levels with radio receiver volume would seem to be virtually infinite, making the decision about what qualifies as true listening perhaps the most vexing challenge at hand.

The issue was brought to light by Nielsen lab tests of Voltair, the controversial audio processor that brought encoding issues to the forefront. In some cases, those tests showed the device enabled “listening” to be credited where the background noise was greater or equal to the audio content being broadcast.

Numeris has been testing Voltair internally but says it has no conclusive results. Canadian broadcasters slammed the brakes on Voltair in mid-June when Numeris asked stations to remove it temporarily. That presumably is making it easier for Numeris to compare Nielsen’s existing code with the enhanced version without Voltair-equipped signals muddying the waters. But it’s not immediately known to what degree broadcasters in Washington and Baltimore have unplugged their Voltairs to provide an apples-to-apples comparison of how the enhanced code and the current code stack up in terms of capturing listening.