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I'm attempting to make a fake choir sound out of sine waves. For the past 5 years, I have been playing around with onlinesequencer.net. It's a very simple and limited online midi music making website with around 50 preset sounds you can use, and some features like different types of distortion, EQ settings, and reverbs, as well as being able to set specific note volumes, detune instruments to any value, etc.

I have an MP3 file of the choir sound I am looking to recreate with the overtone series, but I am looking for a way that I can visualize the overtones and the different volumes of each one, so that I can attempt to recreate the sound on the piano roll, using the 8-bit sine instrument. I would place each overtone at its approximate position on the chromatic scale, and have a hopefully pretty similar version of the choir sound.

I've tried spectrograms, however none that I have used have specific volume values for each overtone, only colors with no key that says what they really mean. If anyone knows a way I can find these volumes, or have a better way of going about this, I would greatly appreciate it. Thank you

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There are many spectrum analyzers that display spectrum on a labeled axis. See e.g., how to do it in Audacity:

https://manual.audacityteam.org/man/plot_spectrum.html enter image description here

If you select a sufficiently short part of a recording (i.e., a single note), you would be able to see the individual harmonic peaks.

Note, that what you're attempting to do is synthesis. While there are no wrong and right ways to synthesize sounds, I would recommend you to learn about synthesis techniques, and tools. There are free software synthesizers available. Some synthesizers, such as free Vital, allow you to edit the volume of each harmonic of the note, which seems like what you are attempting to do.

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  • @Tom For a note with harmonics, phase is irrelevant. Phase may matter when you apply non-linear processing, or mix multiple waveforms for a chorus-like effect. You can display phase by calculating Fourier transform in some more maths focused tools, but that wouldn't be helpful for what OP is trying to do. They could as well use the actual recording and try sample based synthesis in such case. Commented Feb 20, 2023 at 23:35
  • @Tom try it yourself. Note however that synthesizers may normalize the waveforms. As the relative phases affect the maximum amplitude of the waveform, the overall volume may change as you adjust the phases – and that is audible. Commented Feb 21, 2023 at 4:03
  • Hum Indeed. Except for the RMS, nothing hearable. That will change my point of view on additive synthesis !
    – Tom
    Commented Feb 21, 2023 at 6:59
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The FL Studio synthesizer Sytrus can do this, up to 256 harmonics. (This is full-spectrum for any single cycle above roughly E2, 80Hz.) The plugin costs $200, but is included in FL Studio Producer Edition (or above), and can be used for free with the demo version of FL Studio with the restriction that saved projects cannot be re-opened.

Starting with the default preset, select the Operator 1 tab and drag a waveform into the waveform window at the top left. The waveform will be decomposed into sine harmonics and imported as this sum of sine harmonics. Under the "OSC" sub-tab, you can adjust the volume and phase of each harmonic individually.

If you drag in a long sample, you will get a low-resolution re-synthesis of it, which loops on key-press.

Example of long sample imported into Sytrus

This image shows

Waveform
Harmonic Volume
Harmonic Phase

If you drag in a single cycle of a periodic sound, you will get a high-resolution re-synthesis of the overall harmonic makeup. This is the cycle "Vowel U" provided with FL Studio (which is actually 2 cycles, but that's not a major issue):

Example of single cycle sample imported into Sytrus

You will find that any single cycle being looped sounds a lot like an 8-bit "chipsound", rather than the original instrument in the source material. There is a lot more to a sound than the harmonic makeup at a point in time.

A better attempt at synthesizing a choir might be to import a single cycle of a vowel from 6 different singers into each of the 6 operators. This gives you the basic harmonic makeup as well as 6 different voices to which variation can be added.

Add some pitch variation between the operators (by LFO, pitch envelope, random variation, etc), detuned unison (on the main tab), and an overall volume envelope, and you will have a basic synth choir sound. You can thicken this sound even more using unison voices on the main tab.

A related soft synth you should also check out is Harmor, included in FL Studio Signature edition or later, which can resynthesize entire audio files, basically allowing you to use an audio file as the oscillator for an entire synthesizer. It's very powerful, but also very daunting, with the sheer amount of knobs and buttons that can be tweaked.

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