Voice manipulation was the supernatural ability to manipulate the auditory features in one's voice such as pitch, tone and volume to make it sound different, mostly with the intent on deceiving, confusing or threatening others.
- The vampire Collin had capacity to speak with a cold and deepened voice, a fact uncommon for other vampires who retain their human voices. However, he seems to lost it after The Master's fall.
- Vengeance Demons Halfrek and Anyanka each had altered voices at one time. Halfrek used a deepened voice when confusing Xander with a victim and Anyanka had a hoarse, raspy voice when confronting Rupert Giles in her created Wishverse.
- During her phase as a dark witch, Willow Rosenberg screeched at an inhumanly high frequency when on the hunt for Jonathan Levinson and Andrew Wells. Andrew himself said the sound "killed". She later deepened her voice whilst darkening her eyes while claiming "well I've gone pro".
- When the First possessed Willow while she was performing a locator spell, he spoke through her in a loud, booming voice.
- Gachnar used a deepened voice when calling to be released. Later, when the demon appeared in his true form, his voice was proportionately high-pitched.
- The poltergeist Maude Pearson lured Cordelia Chase into her haunted apartment by perfectly imitating Angel's voice on the phone.
- In Jonathan Levinson's alternate world he created where he was a celebrity, Jonathan had an impressive singing voice and his own album to that effect. Since he never showed such a talent in the actual world, this was likely a result of his augmentation spell.
- The demonic contractor Arney could replay anything he heard, mimicing any voice to the exact likeness.
- While in the form as Chloe, the First Evil imitated Buffy's voice, repeating a statement made about the inevitability of Potential Slayers dying.
- When Cordelia was possessed by Jasmine who took on the alias as the Beast's unseen master, she used a loud male voice to pester Angelus and as part of her disguise.
- In order to hide his true identity while posing as Twilight, Angel had Amy Madison cast a spell to alter his voice so it wasn't recognizable.
Voice change via appearance-change
The transition of one's voice to the voice of the shape they assumed was a common component of shapeshifting, transmogrification, possession and even glamours. Some special instances of this included:
- When Pete Clarner would tranform into a beserk version of himself with his formula, his voice became shrill and raspy.
- Rupert Giles, when turned into a Fyarl Demon, spoke the language of the species without initially knowing it and was unable to speak English at that time.
- Jonathan Levinson once used a glamour to make him look like a large demon. Along with this, he also used a more threatening voice.
- When unknowingly transforming into a Wraith-er Demon, Kim would endure brief spasms of transforming into that demon while singing where her voice would change along with her outer appearance.