Natyashastra
स्वरभेदोऽभिनेतव्यो भिन्नगद्गदनिस्वनैः । वेपनात्स्फुरणात्कम्पाद्वेपथुं सम्प्रदर्शयेत् ॥ १०४॥
Change of Voice should be represented by broken and choking voice, and Trembling by quivering, throbbing and shivering.
english translation
svarabhedo'bhinetavyo bhinnagadgadanisvanaiH । vepanAtsphuraNAtkampAdvepathuM sampradarzayet ॥ 104॥
hk transliteration by Sanscript