Table I.

Range of noise and signal-processing conditions tested in the hearing-aid measurements.

Experimental Parameter	Hearing-Aid Processing Hypothesis
SNR: Quiet/10/0 dB	The nonlinear hearing-aid processing, such as noise suppression, is expected to depend on the speech SNR. The external noise is expected to be the strongest factor in the HASPI and HASQI scores, but the scores may also vary across hearing aids depending on how the devices process the noisy speech.
Signal level: 55/65/75 dB SPL	The hearing-aid processing, such as WDRC, is expected to change with the input signal level. Thus the measured amount of distortion may depend on input intensity.
Audiogram: S2/N4	The hearing-aid frequency response and nonlinear processing is dependent on the audiogram. Difference audiograms are expected to tax the hearing-aid amplification to different degrees and to cause different frequency-dependent patterns of nonlinear distortion, and thus produce different HASPI and HASQI values.
Degree of processing: NAL‐R/Mild/Mod/Max	The amount of nonlinear distortion produced by a hearing aid will depend on the type and aggressiveness of the signal processing. Linear processing is expected to give the highest HASPI and HASQI scores, and the maximum processing settings the lowest scores.
Hearing aid manufacturer and model	Different manufacturers use different microphones, receivers, circuitry, and algorithms in their hearing aids. In addition, the signal processing available in premium versus basic devices may differ. These implementation differences are expected to produce differences in measured performance.