Synth plugins?

[rrh]

What I want to be able to do:
Generate a tone that starts at one pitch and shifts to another.
Generate a tone with the pitch modulated by a lower frequency.
Generate a bunch of these and mix them together.

I've only got Audacity recently, but I'm kind of dismayed that I've got a huge list of plugins under "Effects" but a scant handful under "Generate." And when I look through the tutorials, they're all about importing and exporting and filtering and stuff. Nothing about synth. So, maybe Audacity isn't the right tool for me, I don't know? And if it isn't, what is?

[Irish]

What I want to be able to do:
Generate a tone that starts at one pitch and shifts to another.

Audacity 1.3.9 (beta) can do this, but not 1.2.6.
Menu > Generate > Chirp

I would recommend you use 1.3.9. It is as near to a stable version as makes no difference and will shortly be released as version 2.0.

Generate a tone with the pitch modulated by a lower frequency.

I'm not sure if there is a plug-in available for this, but this thread

http://forum.audacityteam.org/viewtopic ... 321#p37321

gives instructions on how to do it.

Edit: I just noticed, what you want is Frequency Modulation, not Amplitude Modulation, which is described in that thread.
I don't know what is available for that, but it certainly can be done.

Once you've generated your tracks, mixing them is just a question of using the Fade and/or Envelope tools.

PO'L

[steve]

1) Upgrade to Audacity 1.3.9 (or whatever the latest release is). Try "Generate > Chirp"

2) Try the "Vocoder" effect. I'm not sure if there are any instructions for this, but you need to make a stereo track with audio to be processed in one channel and the modulation wave in the other. You get a different effect if you change left and right before processing with the vocoder.

3) Look into "Nyquist Programming" http://audacityteam.org/help/nyquist
This is a powerful programming language for audio and is built into Audacity. The really nice thing about it is that programs (scripts) are written in plain text, so you can just use Notepad, or any other plain text editor to write them (Notepad++ is very good - and free).


If the Vocoder does not produce the required modulation effect, you could try using Nyquist to produce the modulation:
1) Use the Generate menu to produce a low frequency tone.
2) Tracks menu > Add New > Audio Track.
3) Use the generate menu to produce a high frequency tone.
4) Click on the name of the upper track and select "Make Stereo Track"
5) Ensure that the track is selected and from the Effects menu select "Nyquist Prompt" (this allows you to type in Nyquist commands without needing to create a plug-in).
6) In the Nyquist prompt box, copy and paste this:

Code: Select all

(mult (aref s 1)(scale 0.5 (sum 1 (aref s 0))))

7) Click "OK"

What it does:
In Audacity Nyquist, stereo sounds are stored as an array.
"s" is a special variable that is used to pass sound from the selection in Audacity to Nyquist.
(aref s 0) is the Left (upper) channel of a stereo track and (aref s 1) is the Right (lower) channel.

(mult ....) multiplies numbers or sound signals
(scale ....) is similar to "mult" but is specific to changing the level of a sound, so (scale 0.5 sound) will halve the volume of a sound.
(sum ....) adds numbers or sounds.

(sum 1 sound) will add 1 to every sample in a sound so that all samples have positive values.
(scale 0.5 sound) scales the sample values by x0.5 so that all sample values are now in the range 0.0 to +1.0
(mult (aref s 1) sound) multiplies (modulates) the Right channel (aref s 1) with our processed sound (from the Left channel)

This gives you amplitude modulation. Frequency modulation is rather more complicated and I'm not sure how you would do that in a simple way. (note to self - must look into frequency modulation).

[Irish]

I'm guessing FM should work on the same basis as Chirp, but using a sine function instead of a linear or Log function to control the pitch.

PO'L

[steve]

Here's a Nyquist script to do frequency modulation - it's a bit more complicated than the AM script, but you use it in exactly the same way.

Code: Select all

(defun variable-resample (mod snd)
  (let ((p1 (log 2.0)) ratio map)
    (setf ratio (s-exp (mult mod p1))) ; pitch ratio
    (setf map (integrate ratio)) ; map from real-time to sound time
    (snd-compose snd (force-srate *sound-srate* map))))

(variable-resample (aref s 0)(aref s 1))

This is based on the "Pitch Change by Resampling Tutorial" by Roger Dannenberg

[steve]

Here's a voice with fm modulation using the script from my previous post. The voice is modulated with a low frequency "chirp" (0.4 Hz to 40 Hz, 1.0 to 0.1 amplitude).
Weird

fm-modulated-voice.mp3.zip

(108.34 KiB) Downloaded 208 times

[rrh]

Okay, knowing those things makes a huge difference, thanks.