Getting better results with G2M/B2M

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Getting better results with G2M/B2M

Postby james » Thu May 27, 2010 4:08 pm

Sonuus pitch-to-MIDI products, including the G2M and B2M, convert the pitch information in an analogue signal into digital MIDI messages. Sometimes you might find the results are not what you expect: the MIDI does not correspond to what you thought you played!

If you are having problems, the following tips will try to explain what is going on and help you to understand what may be happening, allowing you to get better results. Remember, the G2M can't perform magic, it can only convert the signal it's given, not the signal you thought you had sent it!

For brevity, these tips may refer to the G2M or B2M, but apply equally to all Sonuus pitch-to-MIDI products.

Fast real-time detection
When you play your instrument, there are often times where very short notes are produced without you noticing. For example, this can happen as you move from one note to another. You don't notice it because your brain has learned to ignore these things, but these short notes are clearly visible if you record the audio and examine its waveform.

When the G2M sees these short signals, because it is working to minimise latency as much as possible, it has to convert these short notes into MIDI data because it doesn't know at that point in time if the note is going to be short or going to be long. The only way to know for sure would be to wait for longer and add extra latency. These short-duration notes are often referred to as "glitches".

Harmonics and glitches
Glitches (short, high notes) are often caused by real pitches on strings when open-string harmonics are excited, for example when unfretting notes positioned close to a harmonic node. As an example, when a 7th fret note is played then stopped, the act of releasing the 7th fret position while the string is still vibrating can result in the string starting to oscillate at the 7th fret harmonic. This is the same note as the 19th fret position, so you can end up with the note appearing to jump an octave (7th fret to 19th fret). Some instruments are more prone to this than others.

Short-duration harmonics caused in this way will often be ignored by your ear: the first note masks it as long as the new note is not too long. However, because our the pitch detection is so fast, even a very short note will be converted to a MIDI note (because without being able to look into the future, we can't tell how long the note is going to be!). Short notes like this appear to be glitches because you don't notice them when playing normally. But, if you record the audio going into the G2M you will be able to see this sort of thing happening.

Although the G2M is robust against spurious notes, if they are too large or too long they will be detected because they look just like any other intentional note. Here are some tips to help reduce these problems:

(1) Play carefully to avoid these notes: ensure the string has stopped vibrating before unfretting the note. Damping of strings can help with this.

(2) Use the neck pickup rather than the bridge pickup as this is less sensitive to these harmonics.

(3) Turning down the tone control can help, simpy because it reduces the level of these higher notes.

(4) Lighter gauge strings can help because these are easier to damp to avoid unintentional notes being played.

Multiple notes
The G2M is monophonic so it can only process a single note at a time. However, it is robust enough that multiple notes can often be tolerated without adverse effects. But multiple notes become a problem when they are either too loud, so that they start fighting each other, or their pitches are so close that it's not possible to isolate them. This is more of a problem for lower notes because these are more closely spaced in frequency compared to high notes. Therefore, this is often more of a problem for bass players, than guitarists.

Multiple notes can arise in two ways:

(1) When more than one string is played at a time -- non-playing strings are layed by mistake, or are not stopped fully when moving between notes.

(2) Sympathetic vibration where an undamped string resonates with the note being played. When you stop the original note, the sympathetic vibration continues and this can cause problems when you play the next note.

In both cases, careful damping of non-playing strings will reduce these effects to acceptable levels.

Avoid non-pitched sounds
Sounds with no well defined pitch, such as fret buzz, finger noise, string slaps, etc., can often cause problems if they are too obvious. Non-pitched sounds such as these can often appears as short high-frequency notes: glitches.

So ensure your guitar is setup correctly with no fret buzz and always play in such a way to get a correctly pitched note. For example, a bass players often "slap" the strings to evoke a more rhythmic sound and this results in a non-pitched sound before the true note is heard. Because the pitch detection is very fast often the slap has to be interpreted long before the true note begins and this will result in what appears to be wrong notes.

General Tips
(1) Ensure the input signal isn't clipping too much. Some clipping won't affect performance, but if the signal is very clipped, it can compromise detection accuracy. So, if the CLIP LED is on all the time, turn down the instrument's volume.

(2) When switching between instruments, it is a good idea to disconnect and reconnect the cable at the G2M. Doing so will allow the G2M to recalibrate for the new instrument. This is particularly important when switching from a high-output instrument (e.g., a guitar with active pickups) to a low-output instrument (e.g., a guitar with vintage single-coil pickups).

(3) Ensure your guitar is correctly tuned for best note accuracy. Also ensure that intonation is good. Using new strings also helps to improve intonation.

(4) When playing a synthesizer/instrument patch, try to think and play like the sound you are using. For example, when playing a saxophone or cello try to make it sound like the real instrument, not like a guitar. The feedback you get while doing this allows you to adapt your playing style on the fly and allow you to get the best results.
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