  Crowdsourcing micro-task platforms facilitate subjective media quality
assessment by providing access to a highly scale-able, geographically
distributed and demographically diverse pool of crowd workers. Those workers
participate in the experiment remotely from their own working environment,
using their own hardware. In the case of speech quality assessment, preliminary
work showed that environmental noise at the listener's side and the listening
device (loudspeaker or headphone) significantly affect perceived quality, and
consequently the reliability and validity of subjective ratings. As a
consequence, ITU-T Rec. P.808 specifies requirements for the listening
environment of crowd workers when assessing speech quality. In this paper, we
propose a new Just Noticeable Difference of Quality (JNDQ) test as a remote
screening method for assessing the suitability of the work environment for
participating in speech quality assessment tasks. In a laboratory experiment,
participants performed this JNDQ test with different listening devices in
different listening environments, including a silent room according to ITU-T
Rec. P.800 and a simulated background noise scenario. Results show a
significant impact of the environment and the listening device on the JNDQ
threshold. Thus, the combination of listening device and background noise needs
to be screened in a crowdsourcing speech quality test. We propose a minimum
threshold of our JNDQ test as an easily applicable screening method for this
purpose.
