Alien Solo Usage Notes

These notes will help you get the most out of Alien Solo.


The Auto tune section lets you correct any intonation problems that might exist in the input signal. As you increase the Quantize dial, more and more correction is applied, until at the Strict setting all notes will be perfectly in tune. However, this will interfere with any vibrato or slides which might be present. The A dial determines the pitch of middle A, while the 12 Scale buttons select which notes the pitch will be corrected towards.

The Tracking Threshold dial helps the plugin tell difference between a note and no note. When a note is sounding, Alien Solo tries to track its pitch. When there is no note, the envelope settings control whether Alien Solo's own output stops, or decays. Low values are good for very clean recordings, that is, in between the notes you are singing, there is almost no sound at all. Higher values may be needed if there is lots of breath or other noise in between the notes you are singing.
If you have a clean recording, but Threshold is too high, you may lose some of the softer pitch detail.
If you have a noisy recording, but Threshold is too low, Alien Solo might try to interpret some of the noise as a note, and it will probably be the wrong note.

The Tracking Algorithm switch lets you select between two ways of detecting pitch: FFT-based Autocorrelation and Zero-crossing detection. Depending on the type of material, one method might be better than the other listen to both and choose the one you like best. The zero-crossing method uses less CPU power.

The Oscillator 1 controls are pretty straightforward, letting you select the waveform and octave. Transposing one or two octaves down is good for basslines, going up is good for stratospheric lead lines.

The Mode controls how the two oscillators are combined. If you choose the value of Mix, they are simply added together. FM 1<-2 uses the FM algorithm made famous by the DX-7 back in the 80s with one important difference: the modulating waveform isnt a sine wave! If you choose the FM mode, the Osc 2 Level control becomes very important, as if controls the shaping of the tone. Ring mod multiplies the outputs from the two oscillators, and for this method the volume of Osc 2 is disabled.

The Oscillator 2 controls have a couple of extra dials: Detune, which as we all know is good for thickening up the sound, and Volume, to adjust the balance between the two oscillators. If you only want Oscillator 1, set the volume to Off.

The Morphing Filter lets you make the timbre of the synth more organic, interesting, harmonically complex and dynamic. This is the key to creating unique sounds. The idea is similar to a vocoder - you take the formants or harmonics of the input signal, and use them to adjust corresponding portions of the synth signal's spectrum.
The Drive dial lets you "beef up" the harmonics of the original signal before we apply them to the synth sound, while Frequencies and Width control which parts of the original signals spectrum we extract.
The Enharmonic Shift dial lets you apply the original signal's harmonics to a different part of the synth signal's spectrum. If you shift the formants down, it's as if you're applying the vocal characteristics of Darth Vader or Barry White to the synth; while if you shift up, you get to apply Chipmunk-like characteristics.
One important difference is that these shifts are linear, and therefore enharmonic. Things get a little technical here, but the basic idea is that you're not just shifting the formants up or down, you're stretching them apart (if you shift down) or squashing them together (if you shift up).
The final control in this section is Blend. This lets you mix the formant-filtered sound with the raw oscillator signal. A setting of Off means that no Morphing Filter is applied at all (and CPU performance is a little better). 100% means that only formant-filtered sound heard.

The Filter section implements an analogue-style lowpass filter. The Poles buttons let you select how steep the filter is. A 2-pole filter lets quite a lot of high frequencies pass through, giving a "phat" sound reminiscent of the Oberheim synths of the 80s. 4-pole filters give more of a "fat" sound (the two spellings convey so much information!) characteristic of the Moog synths of the 70s. 6-poles? Well, sometimes it's fun to take things to extremes!
The Cutoff controls which frequencies are filtered out, while as expected the Resonance dial controls the emphasis at the cutoff frequency. NB: the 6-pole filters goes into wild self-oscillation at even moderate Resonance settings!
Env Follow and Env Attack let you control how the filter responds to changes in the level of the input signal. An Env Follow value of Off means that the filter ignores the input level. If the Env Attack is Fast, the profile of the input signal is used as is - if you have a strong attack (eg "*D*oo-wop") that that exact envelope is added to the filter cutoff. Med or Slow values mean that the attack (and subsequent decay) is smoothed over, which gives more of an "auto-wah" effect.
The Pitch track dial lets you add the note's pitch to the filter. If this is zero, low notes can sound harmonically richer and high notes relatively mellow. At a setting of 10, an octave jump between two notes will result in an octave jump in the filter's cutoff frequency.

Finally, the Envelope section controls how the amplitude of the output synth sound follows the changing level of the input signal.
If the Follow is set to Off, the envelope is organ-like: there will be 100% signal when a note is on, and silence in between. (See the Tracking Threshold section, above). When the Follow setting is 100% the output level is follows the envelope of the input signal. In between settings cause a mixture of the two extremes.
The Attack control is Fast, the profile of the input signal is used as is - fast attacks in the intput signal mean fast attacks in the output synth signal. Med or Slow values mean that the attack (and subsequent decay) is smoothed over. (This will result in the synth continuing to sound when an input note has finished.)
The Gain control lets you adjust the final output. If the level is too high, it will be soft-clipped. Use the gain control to reduce the level if this happens and you dont like it. Alternatively, you can increase the gain control to get more soft-clipping.

Buffers and Latency

Alien Solo uses FFT (fast fourier transform) to perform pitch tracking and morphing filtering. This is a powerful mathematical technique, but it needs to work on rather large chunks of audio data at once (around 50 milliseconds). However, if you like to use VSTi and DXi soft synths, you probably have your PC and audio host app set up for low latency which means that processing plugins like Alien Solo are only passed very small chunks of data (sometimes less than 10 milliseconds).
If you are running the DirectX version of Alien Solo, and it decides that the buffers are too small, it switches to Buffer Accumulate Mode, and you will see a "BAM" message light up in the preset name window. When this happens, Alien Solo will introduce a very short delay between the input and output, because it has to "accumulate" a buffer full before it can process, meaning that the output data is 50 ms "behind the times".
There are two things you can do about this: (1) go into your host apps audio settings window, and increase the latency/buffer sizes, or (2) drag the audio data 50 ms to the left after processing it.
The VST version of Alien Solo wont exhibit this delay under most hosts, because VST is able to "tell" the host that there is a delay, and the host can compensate by "nudging" things forward a bit.
If the latency is very low, the CPU utilisation of Alien Solo will become erratic. This is easily explained: for most of the time (perhaps four out of every five "little" buffers passed in) the plugin is doing very little work, just "passing on" data that it has already processed. But then once a buffer has accumulated, it does a processing operation on the accumulated "big" chunk. If this uneven CPU usage causes problems, you may need to reduce your latency settings. For most apps this is done with an audio settings dialog, but for Steinberg products like Cubase and Wavelab, you have to go to your soundcard's ASIO settings dialog.


What is Alien Solo?
Alien Solo is a Windows platform plug-in synthesizer which is driven by audio rather than MIDI data. It takes a monophonic vocal line, and produces a synth line that accurately follows the input pitch and envelope. DirectX and VST versions are available.

Is it a DXi / VSTi synthesizer?
No. In terms of VST and DirectX platforms, Alien Solo is not an instrument. It is simply an effect plugin, just like Clone Ensemble and Bass Chorus. However, in terms of the sounds that it produces, an instrument is a good description.

Can I control it with anything other than my voice?
A qualified yes. First of all, it has to be monophonic - no chords. Secondly, Alien Solo is optimized to track frequencies in the 100-1000 Hz range. By limiting the frequency range like this, we can improve the tracking accuracy. So if you give it very high or low pitches, it might behave unpredictably.

I want a deep bassline. Do I have to sing that low?
No. Alien Solo has an octave select switch for both oscillators, so the output bassline can be two octaves below the pitch you sing.

Why is there no LFO?
Alien Solo is designed to let you control the expressive parts of the sound. Want vibrato, tremolo or wah-wah? Sing it!

Um, I don't always sing 100% in key. Do I need to patch an auto-tuning plugin first?
No. Alien Solo can correct your pitch, you can select the scale you're singing in. The only side effect is that your vibrato might also be reduced, and your portamento might turn into glissando.

The Morphing filter seems awfully like a vocoder...
Sometimes, but it has not been designed to be one. The morphing filter is there for one purpose: to allow the synth waveform to be more organic, interesting, harmonically complex and dynamic.

A synth patch that works on one track sounds terrible on another. Why?
Both the Morphing Filter and Filter Envelope are very sensitive to the level of the input signal. If you patch a compressor or limiter plugin before Alien Solo, it might make things more predictable.

What sort of performance does it get?
Alien Solo is quite CPU-hungry. When the Morphing Filter is enabled, it will utilize around 20% of a 733MHz Pentium III. It also requires quite a bit of memory. You won't want to have more than one instance running at once.

What do I get for free?
The unregistered version lets you audition 10 Factory Presets - enough to give you a good idea of its capabilities, but can't twiddle the dials to create your own patches.

Will Alien Solo work with sample rates higher than 44100?
The code is written to work with any sample rate, but I've only tested it at 44100. If you are interested in technical details, the pitch tracking algorithm uses FFT, which requires that buffer sizes be a power of two. This means that there might be slight changes in the way the pitch is tracked between different sample rates. Also remember that at higher rates the CPU usage will go up, and the plug-in has to do more work for each second of audio.

I'm blind, my screen reader has trouble with the knobs and buttons.
In the standard versions on this plugin, the knobs and buttons are all graphical controls. If you prefer, I also have DirectX and VST versions available with plain, focusable controls. Please contact me and I will email them to you directly.


All content and software Copyright 2007 Trevor Magnusson