Is the "tar'eed" (trilling/vibration) in Quranic recitation limited to a trembling in the voice, like shivering from cold, or does it include the rising and falling of vocal tone in prolonged vowels (mudud) without a tremor?

Scholars have clarified that the forbidden tar'eed (trembling) in recitation is the instability of the reciter's voice, like a shiver from cold or pain. As for raising the voice in an extended vowel and lowering it without instability or trembling, this does not fall under the blameworthy tar'eed.