All of the following links have to do with improving voice for PD folks, and also the use of kazoos.

I used to write for this student newspaper:

Music therapy helps tackle Parkinson’s (The Miami Hurricane July 5, 2019)

This is a fairly long honors project paper reviewing voice therapy techniques:

Voice Therapy Techniques in Combination with the Group Therapy Setting for Individuals withParkinson’s Disease

Not necessarily for PD, but the study used spectrographic analysis to measure the improvement in voice in addition to qualitative results.

Finger Kazoo: spectrographic acoustic modifications and vocal self-assessment

I might have already mentioned this in a previous entry, but kazoos were used:

Individual Therapeutic Singing Program for Vocal Quality and Depression in Parkinson’s Disease

Vocal warmups for the individual: Vocal warmups

Vocal warmups for the group: Anatomy of a choral warmup