Re: [LAD] Wavetable synthesis : Creating fat wavetables
On Sat, Aug 25, 2012 at 12:44:12AM +0100, Harry van Haaren wrote: On Fri, Aug 24, 2012 at 11:48 PM, Fons Adriaensen f...@linuxaudio.orgwrote: The easiest way in the case of wavetable synthesis is to upsample your waves by a factor of say 8, then use linear interpolation. So the preparation process is: -record the sounds -upsample x8 Live playing: -downsample the wavetable to the size needed for the frequency that is played Do I understand the steps correctly? Basically just multiply all samples indices by 8. For example if when using the original you would need the value at 3.4, and interpolate between samples 3 and 4, in the upsampled table that becomes 3.4 * 8 = 27.2 and you interpolate between samples 27 and 28. The run-time CPU load is just the same, you only need more memory. But since now you can interpolate witout artefacts, you don't need a perfect fit of K cycles in N samples, and that allows the waves to be shorter. Ciao, -- FA A world of exhaustive, reliable metadata would be an utopia. It's also a pipe-dream, founded on self-delusion, nerd hubris and hysterically inflated market opportunities. (Cory Doctorow) ___ Linux-audio-dev mailing list Linux-audio-dev@lists.linuxaudio.org http://lists.linuxaudio.org/listinfo/linux-audio-dev
Re: [LAD] Wavetable synthesis : Creating fat wavetables
On 08/24/2012 02:21 PM, harryhaa...@gmail.com wrote: Hi everybody! I'm interested in wavetable synthesis, so read around a bit on how they work, best used etc, but I can find preciously little information that You probably know this, but wavetable synthesis is different from a table-lookup oscillator. It sounds like you're doing a table look-up oscillator. describes how to best create a wavetable. Pre-recorded material seems a pretty go-to choice rather than using csound or freinds to generate wavetables. The issue of tuning is where I currently struggle the most: How should that be approached? I wrote a table-lookup oscillator that is currently being used in omap-audio-tool[1] for the tone generator. See [2] for the header. I originally wrote it for fun, with the intention of using it on platforms with weak floating point. Like Fons mentioned in the e-mail, I made my tables a length of N^2 and large enough so that they would not need interpolation for frequencies over about 100Hz (IIRC). Below this cut-off frequency it does linear interpolation. When calculating offsets within your table, it's important to be wary of truncation error (i.e. don't convert your frequency to play every kth sample in the table). This will cause your output frequencies to be different from what you input (quantization error). For generating the tables for sine, triangle, etc., audio-tool has a program generate-wave-table.c[3] that generates the look-up tables in a format suitable for inclusion in a C source file. However, you can easily change the output by changing the 'out()' implementation in main(). -gabriel [1] http://gitorious.org/omap-audio/omap-audio-tool [2] http://gitorious.org/omap-audio/omap-audio-tool/blobs/master/oscillator-table.h [3] I started off calling everything wavetable by mistake, this is one was overlooked in the renaming of thing. ___ Linux-audio-dev mailing list Linux-audio-dev@lists.linuxaudio.org http://lists.linuxaudio.org/listinfo/linux-audio-dev
Re: [LAD] Wavetable synthesis : Creating fat wavetables
On 08/24/2012 10:35 PM, harryhaa...@gmail.com wrote: I record a C3 note, 10 seconds of it. Then I want to create a wavetable. Search for a zero crossing after 1 second, chop. Looped playback = C3. Now I want to have a C#3, so 1/12 of the double of the frequency, playing back at that rate will NOT always provide a C#3. Hi Harry, You may mean the right thing and even have implemented it correctly but a halftone step over base_freq = base_freq * 2^(1/12) Even if you implemented it correctly, overtones or undertones can mislead ones perception quite easily. Looping can warp things back, too. -- I suggest to play the wavetable in a loop and check with a spectrum analyzer if you really have the fundamental. ciao, robin ___ Linux-audio-dev mailing list Linux-audio-dev@lists.linuxaudio.org http://lists.linuxaudio.org/listinfo/linux-audio-dev
Re: [LAD] Wavetable synthesis : Creating fat wavetables
On Fri, Aug 24, 2012 at 08:35:29PM +, harryhaa...@gmail.com wrote: My intention is indeed to do waldorf style cascaded wavetables which are interpolated between. I have a program that I can use to test the wavetables, but the issue of tuning remains a problem for me. A few things to consider. You need an interpolation method that doesn't create artefacts, in this case aliasing. You'll also want it to be fast and efficient. The easiest way in the case of wavetable synthesis is to upsample your waves by a factor of say 8, then use linear interpolation. Takes more memory, but memory is cheap these days. Aeolus does this for pipes that contain significant energy above 1/8 of the sample rate. Provided you have a *good* interpolation method, two things follow. * Your wavetable doesn't need exactly K cycles in N samples, K,N integer. If for example you know you have an integer number of cycles in say 123.4 samples, create a wavetable with 124 samples. On the first iteration, use samples 0...123, then when you reach 124 (beyond the end of the table), jump back 123.4 samples, so interpolate at 0.6, 1.6, 2.6 etc. Similar for all iterations through the loop, the third will be 0.2, 1.2, 2.2 etc. * If you are prepared to e.g. turn a C into a C# by interpolation, then you could as well interpolate to obtain the C. In other words, the wavetable doesn't need to be exactly C in the first place. You just need to know its exact pitch. Picking loop entry/exit points by looking for zero crossings can sometimes provide a reasonable result, but it's pure chance. First, the zero crossings could be everywhere between the samples. Second, the distance between two zero crossings doesn't need to be an exact number of cycles. The easiest way to obtain good loops of natural sounds is to have a playback engine that works as described above, and that allows you to modify the supposed lenght of the loop (the 123.4 in the example) in real time while listening to the result. The alternative is to compute the phase trajectory of the entire waveform, which will tell you the exact pitch with much more precision than looking at the waveform. Whatever the method, the result could be that you have a discon- tinuity between the start and end of the loop. There can be many causes for that. With recorded samples LF noise is one, or the harmonics could simply be not exactly harmonic. In such cases you need to test a different start and end points, until you find some that work well, or to 'bend' the waveform so the ends meet. Ciao, -- FA A world of exhaustive, reliable metadata would be an utopia. It's also a pipe-dream, founded on self-delusion, nerd hubris and hysterically inflated market opportunities. (Cory Doctorow) ___ Linux-audio-dev mailing list Linux-audio-dev@lists.linuxaudio.org http://lists.linuxaudio.org/listinfo/linux-audio-dev
Re: [LAD] Wavetable synthesis : Creating fat wavetables
On Fri, Aug 24, 2012 at 11:18 PM, Robin Gareus ro...@gareus.org wrote: Even if you implemented it correctly, overtones or undertones can mislead ones perception quite easily. Indeed: I've not taken a spectrum analyzer to the signal yet: but something feels wierd with it. Will look at the spectrum and see if the fundamental is present. ___ Linux-audio-dev mailing list Linux-audio-dev@lists.linuxaudio.org http://lists.linuxaudio.org/listinfo/linux-audio-dev
Re: [LAD] Wavetable synthesis : Creating fat wavetables
On Fri, Aug 24, 2012 at 11:48 PM, Fons Adriaensen f...@linuxaudio.orgwrote: The easiest way in the case of wavetable synthesis is to upsample your waves by a factor of say 8, then use linear interpolation. So the preparation process is: -record the sounds -upsample x8 Live playing: -downsample the wavetable to the size needed for the frequency that is played Do I understand the steps correctly? Provided you have a *good* interpolation method, two things follow. You mentioned linear interpolation, I think that will be sufficient considering its an instrument not an emulator, crunchy aliasing? Thats meant to be there :) The alternative is to compute the phase trajectory of the entire waveform, which will tell you the exact pitch with much more precision than looking at the waveform. I don't know how to compute the phase trajectory or that, but it sounds like its not strictly necessary so I'll leave that for the time being. The loop points on the wavetables I'm currently using are just ear picked, and slightly visually tuned. Other concepts I've read about and would be interested in experimenting with after a working prototype is done: -2d interpolation between wavetables and linear interpolation between the wavetables values. Time and phase of wavetables must be exact. -Randomizing phases and loop positions within wavetable for different timbres -Harry PS: Random idea: Create a program which scans trough a short recorded frament, and analyzes the number of samples per cycle. Some sort of take sample, check sample loop should do the trick really, and then output the largest repeated period. That with a sensitivity control is essentially all that's needed to create perfectly looped synthesized recorded wavetables right? ___ Linux-audio-dev mailing list Linux-audio-dev@lists.linuxaudio.org http://lists.linuxaudio.org/listinfo/linux-audio-dev
