Māṇḍūkī Śikṣā 40

40

na cāsya vadato doṣātkañcidapyupalakṣayet
nātyuccaiḥ nāti vā nīcairdoṣeṇa savanasya kham

And when he speaks, no one should perceive any fault in him. / Neither too loud nor too low, nor through a defect of the soma-pressing session, the aperture [of voice],