waveseq – Wave Sequencing User-Defined Opcode for Csound

Lately I’ve been interested in a number of hardware synthesizers that came out during the late 80’s/early 90’s, as I’ve found their synthesis methods rather curious and inventive.  One of them, the Korg Wavestation, has a very interesting synthesis system, using a combination of Vector Synthesis and Wave Sequencing. Vector Synthesis is easy enough to implement using a cross-fading between different oscillators or sound generators, but I was curious to see about implementing the Wave Sequencing in Csound code.

To implement this, I used information obtained online, information in the manuals, time experimenting on a hardware Korg Wavestation, as well as time with the Korg Legacy Wavestation Software (I ended up purchasing the whole Legacy Collection). Here is an example of the waveseq User-Defined Opcode (UDO) using f-tables generated by GEN10:

Example 1:

As well as f-tables using sampled drum sounds:

Example 2:

The UDO is implemented such that it takes in an f-table that describes the entire wave sequence.  Therefore, most of the work to using this opcode is done in creating the set of f-tables to sequence through.  I did implement the following features:

  • Tempo: 24 duration is a quarter note; if tempo is non-zero, it will be used to set the duration of the quarter note, if 0, tempo is about 105 bpm
  • WaveSequence: start wave, looping type (0 = forwards, 1 = forwards and backwards), start wave for loop, end wave
  • Wave Tables: single-cycle wave/single-shot wave/looped wave (determined on whether sample rate given in the waveseq table is 0, positive, or negative), amplitude adjustment, cross-fade time, duration of table to play
About the design, a wave sequence table holds information about how many tables are in the sequence, and how to play them. For example, in example 2, the wave sequence table used is:
itab_bass ftgenonce 0, 0, -9512, 1, "BDRUM11.WAV", 0, 0, 0
itab_tom ftgenonce 0, 0, -17600, 1, "TOM5.WAV", 0, 0, 0
itab_snare ftgenonce 0, 0, -10947, 1, "SNARE11.WAV", 0, 0, 0

iwaveseqtab ftgenonce 0, 0, -32, -2, 3, 1, 0, 0, 2,  
	itab_bass, ftsr(itab_bass), 1, 1, ixfade, iwavedur,  
	itab_tom, ftsr(itab_tom), 2, 1, ixfade, iwavedur,  
	itab_snare, ftsr(itab_snare), 2, 1, ixfade, iwavedur
The iwaveseqtab has 32 size (just needs to be big enough to hold the information for the other tables), and in its first line it describes:
  • 3 tables are in this wave sequence
  • 1 is used to denote backwards and forwards playing through the sequence
  • 0 is the index of the start wave
  • 0 is the index of the loop start
  • 2 is the index of the loop end
after that come the tables to be used.  For example, the part that starts with itab_bass says:
  • sample rate of the table (positive here, so play as single-shot)
  • amplitude adjustment of 1 (amplitude is multiplied by this factor)
  • pitch adjustment of 1 (not currently implemented)
  • crossfade of 0 (ixfade = 0 earlier in the code, not listed above)
  • duration of 6 (iwavedur = 6 earlier in the code, not listed above), this is equivalent to a 16th note
The waveseq UDO is uses the tablexkt opcode, does manual incrementing of phaser variables, use linear amplitude adjustments when cross-fading, and a lot of code for reading from the wave sequence table and configuring things. The code still requires some cleanup work, but I wanted to go ahead and make this initial, mostly-complete implementation available.  I plan to create implement some further features for the waveseq opcode, then create either a full Blue instrument plugin or a BlueSynthBuilder version of this instrument that will allow easier creation and organization of f-tables into wave sequences. I am also thinking about adding Vector Synthesis as well (using then four waveseq instances).
Overall, it was quite an enjoyable experience to study the Wavestation and learn to implement wave sequencing in Csound code.  In the end, I’m still looking at where I might use this opcode in my own work, but it’s nice to know it’s available should I find a use for it.
Download the Examples and MP3’s here: waveseq – example CSD’s and MP3’s


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