What, no control group? I didn't know about that. It looks like we are screwed forever. If there is no control group, how do they know if the treatment works or if the tinnitus just improved by itself?
They used what are known as "active comparators" i.e. other treatment interventions expected to have an effect.
https://clinicaltrials.gov/ct2/show/NCT02669069
Described in the above link
"Active Comparator: PS1 Device: PS1
Participants in this arm shall be given an audio stimulus which comprises of a sequence of tones, mixed with a broadband noise that is spectrally modified to compensate for any hearing loss. Electrical pulses in the somatosensory stimulation are synchronous with the tones.
Active Comparator: PS2 Device: PS2
Participants in this arm shall be given an audio stimulus which comprises of a sequence of tones, mixed with a broadband noise that is spectrally modified to compensate for any hearing loss. Electrical pulses in the somatosensory stimulation are uncorrelated and asynchronous with the tones.
Active Comparator: PS3 Device: PS3
Participants in this arm shall be given an audio stimulus which comprises of a sequence of single-frequency tones mixed with a broadband noise with the frequency characteristics of both chosen outside the region of any hearing loss. Electrical pulses in the somatosensory stimulation are uncorrelated and asynchronous with the tones."
It would have been better if they had used a proper placebo - a "sham" treatment, designed to have no effect on tinnitus. They originally planned to do this- in their 2016 pilot study paper they said, in reference to their big TENT a1 and a2 trials
"These studies will be followed by a Randomised Control Trial to compare this intervention to a sham treatment"-https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5157761/
It may well be there was a perfectly innocent reason they changed their minds about that - I understand a common reason for not using a placebo is you can't "blind" the participants sufficiently i.e. people in the trial might suspect they were getting an intervention designed to have no effect.