In the exam aural tests are conducted from the piano. Every examiner can play piano but most won't be able to play harp.
ABRSM Aural Marks: The pass mark is 12 and the maximum mark is 18. You don't have to pass the aural to pass overall. Distinction: 17–18 - Accurate throughout, Musically perceptive, Confident response Merit: 15–16 - Strengths significantly outweigh weaknesses, Musically aware, Secure response Pass: 12-14 - Strengths just outweigh weaknesses, Cautious response
Trinity Aural Marks Distinction: 9 - 10 - An excellent or very good degree of aural perception in all aspects. Confident and prompt responses. Merit: 8 - A good degree of aural perception in the majority of aspects. Mostly confident and prompt responses. Pass: 6 - 7 - A generally reliable degree of aural perception in most aspects though with some imprecision. Generally confident and prompt responses though with occasional hesitation or uncertainty.
For Digital exams you do not need to take an aural test.
Do not worry if you don't feel like you are a good singer. The examiner is not accessing your singing but your ability to hear pitches and rhythms. So, you need to sing loud and proud every time! And if your nervous remember your never going to see the examiner ever again! The examiner will be happy to adapt to your vocal range, and you can sing to any sound or hum.