21 Oct
2014
21 Oct
'14
3:56 p.m.
Hi
If this
// calculate the next sample: phase ranges from 0 -> 1, but sin()
// expects its input in radians. Just multiply by 2 PI to convert it!
// We also multiply by volume so its not extremely loud.
output[pos] = sin( self->phase * 2 * PI ) * volume;
Sends a sine wave to output (this is the standard sin
<http://www.cplusplus.com/reference/cmath/sin/> math function, right?)
then what would send a square wave? What would send noise?
Thanks -Phil
--
Philippe "xaccrocheur" Coatmeur
http://bitbucket.org/xaccrocheur / https://github.com/xaccrocheur
http://opensimo.org/play/
21 Oct
21 Oct
4:26 p.m.
On Tue, Oct 21, 2014 at 2:56 PM, Philippe Coatmeur <philcm(a)gnu.org> wrote:
Sends a sine wave to output (this is the standard sin
<http://www.cplusplus.com/reference/cmath/sin/> math function, right?)
then what would send a square wave? What would send noise?
If only it were so simple... Sine waves are a single frequency, which makes
it "easy";
-Generate the sine using sin() from <math.h>, input desired freq in rads.
Noise is random().. that's a good hint.
For square waves (or any "complex" signal actually), you need to be aware
of aliasing[1].
There are a number of ways of generating bandlimited square waves, but
"additive synthesis" or adding of sines is probably the best way to learn /
understand aliasing and its effects.
The guys at MusicDSP archives[2] have a variety of oscillators and other
synth building blocks. If you're trying to get things done, I advise using
other peoples code: things get very complex pretty quickly... unless your
aim is to understand this stuff, then merry learning!
I've been doing a wavetable synth[3] which causes aliasing if done wrong
very quickly, again, digging around the internet provides good resources to
learn from.
HTH, -Harry
--
[1] http://en.wikipedia.org/wiki/Aliasing#Sampling_sinusoidal_functions
[2] http://musicdsp.org/archive.php?classid=1
[3] http://openavproductions.com/ninja
http://www.openavproductions.com
4:27 p.m.
Really inefficient and awful sounding version:
output[pos] = (sin (self->phase * 2 * PI ) >= 0 ? 1 : -1) * volume;
Dirty trick: Round the phase increment so that the period becomes an
integer number of sample frames! This produces crystal clear square
waves, but frequency resolution is awful for high frequencies and/or
low sample rates, of course.
The simplest "correct" way is to construct the square wave by adding
up partials (sines), and just stop below Nyqvist, which essentially
brickwall-filters the waveform. Perfect results, but pretty
expensive...
The proper answer is that it's actually really complicated to do this
well, because an ideal geometric waveform contains an infinite number
of partials, and the ones above Nyqvist (sample rate / 2) will be
mirrored down below Nyqvist, making it all sound awful.
Some keywords: band limited oscillator, BLIT, BLEP, minBLEP
You may find interesting code examples here: http://musicdsp.org/
On Tue, Oct 21, 2014 at 3:56 PM, Philippe Coatmeur <philcm(a)gnu.org> wrote:
Hi
If this
// calculate the next sample: phase ranges from 0 -> 1, but sin()
// expects its input in radians. Just multiply by 2 PI to convert it!
// We also multiply by volume so its not extremely loud.
output[pos] = sin( self->phase * 2 * PI ) * volume;
Sends a sine wave to output (this is the standard sin math function, right?)
then what would send a square wave? What would send noise?
Thanks -Phil
--
Philippe "xaccrocheur" Coatmeur
http://bitbucket.org/xaccrocheur / https://github.com/xaccrocheur
http://opensimo.org/play/
_______________________________________________
Linux-audio-dev mailing list
Linux-audio-dev(a)lists.linuxaudio.org
http://lists.linuxaudio.org/listinfo/linux-audio-dev
--
//David Olofson - Consultant, Developer, Artist, Open Source Advocate
.--- Games, examples, libraries, scripting, sound, music, graphics ---.
| http://consulting.olofson.net http://olofsonarcade.com |
'---------------------------------------------------------------------'
4:31 p.m.
On 21/10/14 15:26, David Olofson wrote:
--
Philippe "xaccrocheur" Coatmeur
http://bitbucket.org/xaccrocheur / https://github.com/xaccrocheur
http://opensimo.org/play/
Really inefficient and awful sounding version:
output[pos] = (sin (self->phase * 2 * PI ) >= 0 ? 1 : -1) * volume;
Dirty trick: Round the phase increment so that the period becomes an
integer number of sample frames! This produces crystal clear square
waves, but frequency resolution is awful for high frequencies and/or
low sample rates, of course.
The simplest "correct" way is to construct the square wave by adding
up partials (sines), and just stop below Nyqvist, which essentially
brickwall-filters the waveform. Perfect results, but pretty
expensive...
The proper answer is that it's actually really complicated to do this
well, because an ideal geometric waveform contains an infinite number
of partials, and the ones above Nyqvist (sample rate / 2) will be
mirrored down below Nyqvist, making it all sound awful.
Some keywords: band limited oscillator, BLIT, BLEP, minBLEP
You may find interesting code examples here: http://musicdsp.org/
On Tue, Oct 21, 2014 at 3:56 PM, Philippe Coatmeur <philcm(a)gnu.org> wrote:
Wow, that was quick. This (and Harry's infos) is exactly what I need,
thanks a lot LADs.
--Phil
Hi
If this
// calculate the next sample: phase ranges from 0 -> 1, but sin()
// expects its input in radians. Just multiply by 2 PI to convert it!
// We also multiply by volume so its not extremely loud.
output[pos] = sin( self->phase * 2 * PI ) * volume;
Sends a sine wave to output (this is the standard sin math function, right?)
then what would send a square wave? What would send noise?
Thanks -Phil
--
Philippe "xaccrocheur" Coatmeur
http://bitbucket.org/xaccrocheur / https://github.com/xaccrocheur
http://opensimo.org/play/
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3 comments
3 participants
participants (3)
-
David Olofson -
Harry van Haaren -
Philippe Coatmeur