[sdiy] Building a Better Bass Patch

[harry bissell]

Woah I'll have to do this inline :^)

Tim Daugard wrote:
> I do it the easy way. All my patches start at the bass guitar. From observing the
> waveforms through my system, I have obsereved that a reall basse starts out with strong
> harmonics. The harmonics die off over a period of time.
>
> The waveforms don't show significant phasing (I know maybe to small to see). Proof of this
> might be the method of tuning the bass with harmonics. Once the bass is properly tuned
> using the harmonics the two tone can run for a long time without beating.
>   
Watch the amplitude envelope over the whole length of the note. You will 
see that the amplitude decreases...
then increases again. Another clue is that there will be "rolling" peaks 
and multiple zero crosses. There should be
one negative, and one positive peak per cycle... and only one zero cross 
per cycle.  However you will get one
major and one minor peak on a half cycle... these change amplitude with 
time so the minor one overtakes
the major one.  This is the effect that kills almost every attempt at 
pitch recognition.  I find the cause is the
harmonics are sharp due to string stiffness (non-ideal string) and that 
three harmonics are enough to show it
in all its (nefarious) glory.
> So, I believe:
>
> - The primary tone is the first (fundamental) and third harmonics. I offer as proof, the
> fact that taking a bass note and adding the divide by two signal doesn't do much for the
> tone. Divide by three and add and you get a wonderful deep rich sound.
>
> http://home.earthlink.net/~synthfred/h_fdv101.htm
>
> - The third harmonic dies relatively quickly - can be heard in a whole note and definitly
> in a note held for two bars.
>
> Start with a square wave, or a sawtooth filter heavily to get the fundamenta and just a
> few of the harmonics, then follow with a envelope controlled filter to further cut the
> harmonics as time goes on.
>   
Start with a sawtooth is a better idea IMHO. I synthesize from a 
sawtooth, but can substitute a triangle wave.
If you want an electronic bass sound, square or triangle is ideal, for a 
bass guitar sawtooth works much better.
> - Fat of the finger verses nail / pick plucking makes a difference in the initial sound
>
> Add a pulse from the trigger source.
>
> Add a signal two or three octaves up (in sync) with a very short envelope - 0 attack time
> 32nd or 64th note length decay time. Decay to 0, no sustain or release.
>
> - The tone swells in the first few cycles. I've never figured this out, but sitting here
> now, it maybe a result of the build up of the mag/elec field in the pickup? My acoustic
> basses respond faster, but that could be strings, technique (more effort required to get a
> good volume tone), wood tone.
>   
The initial attack is an impulse. You 'whack' the string and all 
harmonics are excited. Higher ones die
instantly... but think,,, it takes probably 24ms for a single cycle of 
fundamental to appear at all. The
energy from the whack is transformed by the resonant modes of the string 
into discrete frequencies
(of course with sharp harmonics).  Your added transient simulates the 
non-harmonic attack...
> If you use multiple oscillators, the higher pitches have faster attacks. The fundamental
> should take 2 to 3 cycles to hit full volume.
>
> - The note never ends on a good bass guitar. Even without feedback a note can be held for
> two bars, three bars, or even longer. part of the bass technique is muting notes as you
> are done with them. I don't play stand up bass so I can't speak for them. I would say that
> from listening to them, most of this applies, however, the notes do end relatively
> quickly. A plucked note on a standup ends in less than a quarter note.
>   
I use an asymmetrical (has DC level) sawtooth.  You might describe it as 
a triangle with a fast rise and slow fall.
The first couple of cycles overdrive the circuit and are clipped, then a 
Vactrol based LPF rolls off the high frequencies fast. I have some scope 
photos.. they used to be up at guitarfool.com but they have been removed 
now. Maybe they are still at archive.org ?

Can't we all bitch at each other just a little... like how to make a 
bass guitar sound using only a
'phat' Minimoog ???  (like the freindly folk at AH ??? :^)

H^) harry