Adding More Pipes


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A single pipe isn’t a very interesting sound.  An organ’s richness comes from playing multiple pipes when a key is pressed.


We’ll follow this path in two steps.  First, we’ll add a single 2’ pipe to the patch.  Second, we’ll build a patch with five pipes per key.




What Are Those ‘ Markings, Anyway?


Let’s take a moment to talk about how pipes are named.  A “rank” of pipes is typically a group of 61 pipes, tuned to the chromatic scale.  61 pipes are 5 octaves, and most organs have 5-octave keyboards.


A typical 5-octave organ keyboard plays the notes between C2 and C7.  A piano has two additional octaves, one below and one above, and plays the notes between C1 and C8.


It turns out that if you build a pipe that plays the C2 pitch, it’s about 8 feet high.  And that’s where the 8’ name comes from:  it’s the length of the longest pipe in the rank.  There’s more to it than that, but that’s the historical background behind the naming convention.


The rich sound of a pipe organ is usually achieved by playing multiple pipes at once, tuned apart by octaves, or fifths.  It’s like having multiple oscillators on a synthesizer, and tuning them apart by octaves:  it makes a full sound.


An 8’ rank of pipes is the “standard” length.  That is, the pitches correspond to the middle 5 octaves of a piano keyboard.  Many pipe organs have other ranks available:  16’, 4’, 2’, 1’, and 2 2/3’ are common lengths.  These names also correspond to the longest pipe in the rank.  That is, a 16’ rank of pipes will play pitches that are one octave lower than an 8’ rank.  A 4’ rank will play pitches that are one octave higher than an 8’ rank.  A 2’ rank will be two octaves higher, a 1’ rank will be 3 octaves higher, and a 2 2/3’ rank will be one octave and a fifth higher (between the 4’ and 2’ pipes).


Hey, these names match the drawbar names on a Hammond organ!  Yep, Laurens Hammond named his drawbars after organ pipes.




Adding a 2’ Pipe


Our first change will be the addition of a 2’ pipe.  This is a pipe that’s tuned two octaves above the first pipe.  It makes a distinctive pipe organ sound, without requiring a lot of additional DSP power.  Notice that the comb filter delay for the 2’ pipe is tuned two octaves higher than the 8’ comb filter delay.


The patch is below.  The second picture is the FX area which contains a pipe mixer and a reverb module.







Creating a decent-sounding pipe sound across five octaves presents some challenges.  These are:


  • High-pitched pipes won’t play unless the lowpass filter is opened up.  But the lowpass filter needs to be closed down at the bottom of the keyboard, so the notes don’t sound too “clarinetty”.  This is why the lowpass filter has its own SeqCtr.  Remember, any manipulation of this filter’s frequency requires re-tuning.


  • The highpass filter is necessary to remove the DC “thunk” at the start of a note.  This, too, needs some tracking.  If its cutoff frequency is too low, the note will “thunk”.  But if it’s too high, the note will sound thin.  Ideally, another SeqCtr could be used to fine-tune the filter, but that would eat up more DSP.




A Five-Pipe Patch


Now, we’re going to be more ambitious, and attempt a five-pipe patch.  These pipes will be tuned in octaves:  16’, 8’, 4’, 2’, and 1’.  Creating the basic patch is as simple as cutting and pasting one of the existing pipes.  The time-consuming work is that each pipe must then be filtered and tuned until it sounds acceptable across the keyboard.


Here is where we’ll run into the G2’s polyphony limitations.  A single one of these five-pipe notes requires an entire DSP.  That means a standard G2 can play only four notes at a time.  If we add an FX area containing reverb, the polyphony is reduced to three notes.  Ugh.  That’s not enough for any serious organ music.  This patch will benefit greatly from the G2’s expansion card.


A portion of the patch is shown below.  We’ll mix the pipes using the 6-channel stereo mixer with pan.  That lets us pan each pipe in the stereo field, if we wish.  All 8 variations are programmed with different combinations of pipes.





The above patch contains the reverb module, so is limited to 3 notes on an unexpanded G2.  For those with outboard reverb units, here is the same patch without the reverb.  It provides an additional note of polyphony.