Possible to preserve formants when changing pitch?

[Turkrosoft]

Is it possible to preserve the formants when adjusting pitch? Many TTS engines support that. There may also be two separate modes or a check box letting the user adjust the pitch by or without effecting the formants.

[rmcpantoja]

In fact, I was able to do this in a Discord bot for Piper using praat-parcelmout. Here's a code snippet:

def change_pitch_with_praat(audio_file, factor):
    snd = parselmouth.Sound(audio_file)
    manipulation = call(snd, "To Manipulation", 0.01, 75, 600)
    pitch_tier = call(manipulation, "Extract pitch tier")
    call(pitch_tier, "Multiply frequencies", snd.xmin, snd.xmax, factor)
    call([pitch_tier, manipulation], "Replace pitch tier")
    return call(manipulation, "Get resynthesis (overlap-add)")

async def piper(
    interaction: discord.Interaction,
    voice: str,
    speaker: Optional[int] = 0,
    rate: Optional[float] = 1.00,
    pitch: Optional[float] = 1.00,
    text: Optional[str] = "This is a test."
):
    loop = asyncio.get_event_loop()
    await interaction.response.send_message(f'Text-To-Speech request sent by {interaction.user.mention}.\nStarting...', ephemeral=True)
    task = loop.create_task(piper_thread(discord.Interaction, voice, speaker, rate, text))
    wav_filename = await task
    if wav_filename == -1:
        await interaction.channel.send(f'This voice doesn't exists! Please use /list to get a list. The voice was: {voz}.')
        return
    utc_now = datetime.datetime.now(timezone.utc)
    if pitch != 1.00:
        print(pitch)
        audio = change_pitch_with_praat(wav_filename, pitch)
        wav_filename = f"{wav_filename[:-4]}_changed.wav"
        audio.save(wav_filename, "WAV")
    if (utc_now - interaction.created_at).total_seconds() < 900:
        if len(text) > 1500:
            realtest = "Large text."
        else:
            realtest = text
        await interaction.channel.send (f"{interaction.user.mention}, this is your audio generated with {voice}!\nText: {realtest}", file=discord.File(wav_filename))
    else:
        print("Error! The interaction has expired and a response can't be sent.")