Re: [music-dsp] wavetable filtering

[robert bristow-johnson]

On 7/3/18 7:23 AM, alexandre niger wrote:


Thank you for all the help. Gain loss was finally fixed after 
normalizing.
In an other hand, using fft and inverse effectively gave better 
results than FIR or IIR. With very rich signals, I can still hear an 
harmonic difference between WTs. I guess I could fix it by using more 
WTs than one every octave. I will try every 6 semitones.


other times this topic has come up, i have said exactly that.  if your 
sample rate is 48 kHz and you're willing to settle for a top bandwidth 
of 19.8 kHz, (so with a fixed LPF you are gonna kill anything that 
survives between 19.9 and 24 kHz, two wavetables per octave will do it.  
so at the bottle of the 6 semitone split, your wavetable will have 
harmonics up to 19 kHz, as you increase the pitch to 6 semitones higher 
(that's a frequency ratio of sqrt(2)), that 19.8 kHz becomes 28.1 kHz, 
which folds over (reflects about 24 kHz) to 19.9 kHz.  that's your worst 
case.  so just blow away everything above 19.8 kHz with a single fixed 
and sharp LPF. but since memory is cheap, there should be no reason you 
can't go to 3 wavetables per octave.  or not even an integer.  say one 
wavetable for every 5 semitones.  no reason you can't do that either.


with 96 kHz sample rate, it's much less of a problem regarding aliasing 
above 24 kHz and you can relax your specs with that LPF and the number 
of wavetables per octave.


i would suggest mixing or crossfading from the wavetable that is richer 
in harmonics to the wavetable missing a few as your note slides up and 
down the keyboard.  like if you have a wavetable at every C and every 
F#, when the note is F, it should be 1/6 scaling the wavetable at C and 
5/6 scaling the wavetable at F#.  when the note is an A, it should be 
1/2 of the wavetable at the F# below and 1/2 of the wavetable at C above.


--

r b-j  r...@audioimagination.com

"Imagination is more important than knowledge."



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Re: [music-dsp] wavetable filtering

[alexandre niger]

Thank you for all the help. Gain loss was finally fixed after normalizing. 
In an other hand, using fft and inverse effectively gave better results than 
FIR or IIR. With very rich signals, I can still hear an harmonic difference 
between WTs. I guess I could fix it by using more WTs than one every octave. I 
will try every 6 semitones. 
Best, 
Alex 


De: "alexandre niger"  
À: "music-dsp"  
Envoyé: Vendredi 29 Juin 2018 16:17:47 
Objet: [music-dsp] wavetable filtering 


Hello everyone, 

I just joined the list in order to find help in making a wavetable synth. This 
synth would do both morphing and frequency wavetables. Morphing is a way to 
play different waveforms over time and so to get an additional sound dimension. 
Frequency wavetables are used to avoid aliasing by filtering harmonics the 
higher the frequency go. I started with the frequency wavetables and then I 
will do the morphing between different waveforms. 

As an intern at Rebel Technology, I started making wavetables patches from 
earlevel articles. In those patches, common waveforms are generated inside the 
code (tri, square, saw). Now I want to generate some more complex waveforms 
from an editor called WaveEdit (free). They come as 256 samples single cycle 
.wav files. Then I change them into static data in a header file. Once I have 
this, I can start with frequency wavetables. The key point of frequency 
wavetables is the filtering. I have to filter enough harmonics so the aliased 
frequencies do not come back under 18KHz (audiable range). But I must not 
filter too much if I don't want to get gain loss. 

At the moment I managed to make a 3550 taps FIR to filter every octave 
wavetables. Unfortunately, with complex harmonic rich waveforms, I still have 
audiable aliasing from 2kHz and gain/amplitude difference when wavetables 
cross. 
So now I am wondering: 
About aliasing, should I cascade two FIR instead of increasing the taps? 
That could be a solution if the stop band is not attenuated enough. According 
to octave fir1, stop band attenuation is 50dB to 70dB. 
About gain loss, will "harmonic rich signal" always sound lower when filtered 
even if gain is the same? 
I haven't normalize wavetables yet. I might have my answer afterwards. 

You can have a look at the patch code but you won't be able to try it if you 
don't get Rebel Technology Owl files. 
https://github.com/alexniger/OLWpatches-RebelTech/blob/master/WTExtWavePatch.hpp
 
All other links are in the readme. 

Best, 

Alex 


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Re: [music-dsp] wavetable filtering

[gm]

7th octave, but 127th harmonic

harmonics are not octaves but multiples of the fundamental


Am 01.07.2018 um 14:00 schrieb Martin Klang:


I'm surprised it only outputs 256 sample waveforms. Does that not mean 
that you can only go up to the 7th harmonic?




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Re: [music-dsp] wavetable filtering

[Martin Klang]

I recommended to Alex that he use the output from Andrew Belt's WaveEdit 
after reading about it here (9 March 2018 "Wavetable File Formats").


I'm surprised it only outputs 256 sample waveforms. Does that not mean 
that you can only go up to the 7th harmonic?



Martin


On 29/06/18 17:40, Nigel Redmon wrote:

Hi Alexandre,

A couple of comments:

It looks like you’re saying that you’re taking the 256-sample 
wavetables, and want to create addition levels of bandlimited version 
fo them, but using time-domain filtering. It would be better to take 
and FFT, and manipulating the harmonics int he frequency domain. 
Because these are single-cycle waveform, manipulation in the frequency 
domain (e.g., zeroing out highs “bins”) will produce perfect results. 
That is, if you have a harmonic-rich wavetable from WaveEdit, and you 
want to make a version that can be transposed up an octave without 
aliasing, FFT the wave, zero out the upper half of the terms, iFFT 
 back to a wavetable. Of course, you only need to convert it to the 
frequency domain ones, then make as many “filtered” copies of it as 
you want.


Note that 256 is a small wavetable. As pointed out in my articles, you 
can’t get both low frequencies and high harmonics with such a small 
table. A 256-sample sawtooth played at 40 Hz will sound dull (lowpass 
filtered).


Regards,

Nigel

On Jun 29, 2018, at 7:19 AM, alexandre niger 
mailto:alexandre.ni...@ensea.fr>> wrote:



Hello everyone,

I just joined the list in order to find help in making a wavetable 
synth. This synth would do both morphing and frequency wavetables. 
Morphing is a way to play different waveforms over time and so to get 
an additional sound dimension. Frequency wavetables are used to avoid 
aliasing by filtering harmonics the higher the frequency go. I 
started with the frequency wavetables and then I will do the morphing 
between different waveforms.


As an intern at Rebel Technology, I started making wavetables patches 
from earlevel articles. In those patches, common waveforms are 
generated inside the code (tri, square, saw). Now I want to generate 
some more complex waveforms from an editor called WaveEdit (free). 
They come as 256 samples single cycle .wav files. Then I change them 
into static data in a header file. Once I have this, I can start with 
frequency wavetables. The key point of frequency wavetables is the 
filtering. I have to filter enough harmonics so the aliased 
frequencies do not come back under 18KHz (audiable range). But I must 
not filter too much if I don't want to get gain loss.


At the moment I managed to make a 3550 taps FIR to filter every 
octave wavetables. Unfortunately, with complex harmonic rich 
waveforms, I still have audiable aliasing from 2kHz and 
gain/amplitude difference when wavetables cross.

So now I am wondering:
About aliasing, should I cascade two FIR instead of increasing the taps?
That could be a solution if the stop band is not attenuated enough. 
According to octave fir1, stop band attenuation is 50dB to 70dB.
About gain loss, will "harmonic rich signal" always sound lower when 
filtered even if gain is the same?

I haven't normalize wavetables yet. I might have my answer afterwards.

You can have a look at the patch code but you won't be able to try it 
if you don't get Rebel Technology Owl files.

https://github.com/alexniger/OLWpatches-RebelTech/blob/master/WTExtWavePatch.hpp
All other links are in the readme.

Best,

Alex


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Re: [music-dsp] wavetable filtering

[robert bristow-johnson]

�
you don't really need symmetric to prevent phase cancellations.� you just need 
to make the phases of each harmonic (and in wavetable synthesis, **each** 
partial or overtone is harmonic) of the two wavetables that you're crossfading 
or blending to be aligned.
what even
symmetry does is line up all of the harmonics represented as cosines all with 
phase of zero.� or odd symmetry lines up all of the harmonics as sines with 
phase of zero.� since they all have phase of zero, they're all lined up.� but 
if you extract the wavetables from a sampled note,
your waveshape will likely have neither even nor odd symmetry.� and sometimes 
phase is salient; it affects the waveshape.� so unlike Andrew Horner, i would 
not toss the phase information for each harmonic to the wind.� i would preserve 
that information.
you can circularly shift
a wavetable and keep its waveshape.� a good way to optimally align the phase of 
the harmonics (without disassembling the wave into harmonics and changing the 
waveform by shifting harmonics independently) is to *circularly* 
cross-correlate one wavetable with the other.� the correlation lag
that gives you the maximum (positive) correlation is the lag value used to 
"spin" or "rotate" one wavetable w.r.t. the other to line up the waveforms.
if sequential wavetables are extracted directly from a sampled note (with 
waveshape and timbre that evolves in time after
the onset), this is what you would do anyway.� the set of wavetables **should** 
be aligned when you load them ready to rock-n-roll in your wavetable synth.



 Original Message 

Subject: Re: [music-dsp] wavetable filtering

From: "gm" 

Date: Fri, June 29, 2018 7:39 am

To: music-dsp@music.columbia.edu

--



> You could use FFT where you can also make the waves symmetric

> which prevents phase cancellations when you blend waves.

>

>

> Am 29.06.2018 um 16:19 schrieb alexandre niger:

>>

>> Hello everyone,

>>

>> I just joined the list in order to find help in making a wavetable

>> synth. This synth would do both morphing and frequency wavetables.

>> Morphing is a way to play different waveforms over time and so to get

>> an additional sound dimension. Frequency wavetables are used to avoid

>> aliasing by filtering harmonics the higher the frequency go. I started

>> with the frequency wavetables and then I will do the morphing between

>> different waveforms.

>>

>> As an intern at Rebel Technology, I started making wavetables patches

>> from earlevel articles. In those patches, common waveforms are

>> generated inside the code (tri, square, saw). Now I want to generate

>> some more complex waveforms from an editor called WaveEdit (free).

>> They come as 256 samples single cycle .wav files. Then I change�them

>> into static data in a header file. Once I have this, I can start with

>> frequency wavetables. The key point of frequency wavetables is the

>> filtering. I have to filter enough harmonics so the aliased

>> frequencies do not come back under 18KHz (audiable range). But I must

>> not filter too much if I don't want to get gain loss.

>>

>> At the moment I managed to make a 3550 taps FIR to filter every octave

>> wavetables. Unfortunately, with complex harmonic rich waveforms, I

>> still have audiable aliasing from 2kHz and gain/amplitude difference

>> when wavetables cross.

>> So now I am wondering:

>> About aliasing, should I cascade two FIR instead of increasing the taps?

>> That could be a solution if the stop band is not attenuated enough.

>> According to octave fir1, stop band attenuation is 50dB to 70dB.

>> About gain loss, will "harmonic rich signal" always sound lower when

>> filtered even if gain is the same?

>> I haven't normalize wavetables yet. I might have my answer afterwards.

>>

>> You can have a look at the patch code but you won't be able to try it

>> if you don't get Rebel Technology Owl files.

>> https://github.com/alexniger/OLWpatches-RebelTech/blob/master/WTExtWavePatch.hpp

>> All other links are in the readme.

>>

>> Best,

>>

>> Alex

>>

>>

>>

>>

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>> dupswapdrop: music-dsp mailing list

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>

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�
�
�


--



r b-j� � � � � � � � � � � � �r...@audioimagination.com



"Imagination is more important than knowledge."

�
�
�
�
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Re: [music-dsp] wavetable filtering

[Nigel Redmon]

Hi Alexandre,

A couple of comments:

It looks like you’re saying that you’re taking the 256-sample wavetables, and 
want to create addition levels of bandlimited version fo them, but using 
time-domain filtering. It would be better to take and FFT, and manipulating the 
harmonics int he frequency domain. Because these are single-cycle waveform, 
manipulation in the frequency domain (e.g., zeroing out highs “bins”) will 
produce perfect results. That is, if you have a harmonic-rich wavetable from 
WaveEdit, and you want to make a version that can be transposed up an octave 
without aliasing, FFT the wave, zero out the upper half of the terms, iFFT  
back to a wavetable. Of course, you only need to convert it to the frequency 
domain ones, then make as many “filtered” copies of it as you want.

Note that 256 is a small wavetable. As pointed out in my articles, you can’t 
get both low frequencies and high harmonics with such a small table. A 
256-sample sawtooth played at 40 Hz will sound dull (lowpass filtered).

Regards,

Nigel

> On Jun 29, 2018, at 7:19 AM, alexandre niger  wrote:
> 
> 
> Hello everyone,
> 
> I just joined the list in order to find help in making a wavetable synth. 
> This synth would do both morphing and frequency wavetables. Morphing is a way 
> to play different waveforms over time and so to get an additional sound 
> dimension. Frequency wavetables are used to avoid aliasing by filtering 
> harmonics the higher the frequency go. I started with the frequency 
> wavetables and then I will do the morphing between different waveforms.
> 
> As an intern at Rebel Technology, I started making wavetables patches from 
> earlevel articles. In those patches, common waveforms are generated inside 
> the code (tri, square, saw). Now I want to generate some more complex 
> waveforms from an editor called WaveEdit (free). They come as 256 samples 
> single cycle .wav files. Then I change them into static data in a header 
> file. Once I have this, I can start with frequency wavetables. The key point 
> of frequency wavetables is the filtering. I have to filter enough harmonics 
> so the aliased frequencies do not come back under 18KHz (audiable range). But 
> I must not filter too much if I don't want to get gain loss.
> 
> At the moment I managed to make a 3550 taps FIR to filter every octave 
> wavetables. Unfortunately, with complex harmonic rich waveforms, I still have 
> audiable aliasing from 2kHz and gain/amplitude difference when wavetables 
> cross.
> So now I am wondering:
> About aliasing, should I cascade two FIR instead of increasing the taps? 
> That could be a solution if the stop band is not attenuated enough. According 
> to octave fir1, stop band attenuation is 50dB to 70dB.
> About gain loss, will "harmonic rich signal" always sound lower when filtered 
> even if gain is the same?
> I haven't normalize wavetables yet. I might have my answer afterwards. 
> 
> You can have a look at the patch code but you won't be able to try it if you 
> don't get Rebel Technology Owl files.
> https://github.com/alexniger/OLWpatches-RebelTech/blob/master/WTExtWavePatch.hpp
> All other links are in the readme.
> 
> Best,
> 
> Alex
> 
> 
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Re: [music-dsp] wavetable filtering

[gm]

You could use FFT where you can also make the waves symmetric
which prevents phase cancellations when you blend waves.


Am 29.06.2018 um 16:19 schrieb alexandre niger:


Hello everyone,

I just joined the list in order to find help in making a wavetable 
synth. This synth would do both morphing and frequency wavetables. 
Morphing is a way to play different waveforms over time and so to get 
an additional sound dimension. Frequency wavetables are used to avoid 
aliasing by filtering harmonics the higher the frequency go. I started 
with the frequency wavetables and then I will do the morphing between 
different waveforms.


As an intern at Rebel Technology, I started making wavetables patches 
from earlevel articles. In those patches, common waveforms are 
generated inside the code (tri, square, saw). Now I want to generate 
some more complex waveforms from an editor called WaveEdit (free). 
They come as 256 samples single cycle .wav files. Then I change them 
into static data in a header file. Once I have this, I can start with 
frequency wavetables. The key point of frequency wavetables is the 
filtering. I have to filter enough harmonics so the aliased 
frequencies do not come back under 18KHz (audiable range). But I must 
not filter too much if I don't want to get gain loss.


At the moment I managed to make a 3550 taps FIR to filter every octave 
wavetables. Unfortunately, with complex harmonic rich waveforms, I 
still have audiable aliasing from 2kHz and gain/amplitude difference 
when wavetables cross.

So now I am wondering:
About aliasing, should I cascade two FIR instead of increasing the taps?
That could be a solution if the stop band is not attenuated enough. 
According to octave fir1, stop band attenuation is 50dB to 70dB.
About gain loss, will "harmonic rich signal" always sound lower when 
filtered even if gain is the same?

I haven't normalize wavetables yet. I might have my answer afterwards.

You can have a look at the patch code but you won't be able to try it 
if you don't get Rebel Technology Owl files.

https://github.com/alexniger/OLWpatches-RebelTech/blob/master/WTExtWavePatch.hpp
All other links are in the readme.

Best,

Alex




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[music-dsp] wavetable filtering

[alexandre niger]

Hello everyone, 

I just joined the list in order to find help in making a wavetable synth. This 
synth would do both morphing and frequency wavetables. Morphing is a way to 
play different waveforms over time and so to get an additional sound dimension. 
Frequency wavetables are used to avoid aliasing by filtering harmonics the 
higher the frequency go. I started with the frequency wavetables and then I 
will do the morphing between different waveforms. 

As an intern at Rebel Technology, I started making wavetables patches from 
earlevel articles. In those patches, common waveforms are generated inside the 
code (tri, square, saw). Now I want to generate some more complex waveforms 
from an editor called WaveEdit (free). They come as 256 samples single cycle 
.wav files. Then I change them into static data in a header file. Once I have 
this, I can start with frequency wavetables. The key point of frequency 
wavetables is the filtering. I have to filter enough harmonics so the aliased 
frequencies do not come back under 18KHz (audiable range). But I must not 
filter too much if I don't want to get gain loss. 

At the moment I managed to make a 3550 taps FIR to filter every octave 
wavetables. Unfortunately, with complex harmonic rich waveforms, I still have 
audiable aliasing from 2kHz and gain/amplitude difference when wavetables 
cross. 
So now I am wondering: 
About aliasing, should I cascade two FIR instead of increasing the taps? 
That could be a solution if the stop band is not attenuated enough. According 
to octave fir1, stop band attenuation is 50dB to 70dB. 
About gain loss, will "harmonic rich signal" always sound lower when filtered 
even if gain is the same? 
I haven't normalize wavetables yet. I might have my answer afterwards. 

You can have a look at the patch code but you won't be able to try it if you 
don't get Rebel Technology Owl files. 
https://github.com/alexniger/OLWpatches-RebelTech/blob/master/WTExtWavePatch.hpp
 
All other links are in the readme. 

Best, 

Alex 


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