# Generating sin/square waves sound

P

#### Paulo da Silva

Hi,
Sorry if this is a FAQ, but I have googled and didn't find any

Is there a simple way, preferably multiplataform (or linux), of
generating sinusoidal/square waves sound in python?

8

#### 88888 Dihedral

Please check PYGAME and Simple Directmedia library.

Python is used as the director like role and functions in SDL
do most of the jobs in Pygame.

D

#### Dave Angel

Hi,
Sorry if this is a FAQ, but I have googled and didn't find any

Is there a simple way, preferably multiplataform (or linux), of
generating sinusoidal/square waves sound in python?

If you're willing to be Linux-only, then I believe you can do it without
any extra libraries.

You build up a string (8 bit char, on Python 2.x) of samples, and write
it to "/dev/audio". When i experimented, I was only interested in a
few seconds, so a single write was all I needed.

Note that the samples are 8 bits, and they are offset by 128. So a zero
signal would be a string of 128 values. A very quiet square wave might
be a bunch of 126, followed by a bunch of 130. and so on. And the
loudest might be a bunch of 2's followed by a bunch of 253's.

You'll have to experiment with data rate; The data is sent out at a
constant rate from your string, but I don't know what that rate is.

M

#### mblume

Am Fri, 30 Dec 2011 07:17:13 +0000 schrieb Paulo da Silva:
Hi,
Sorry if this is a FAQ, but I have googled and didn't find any

Is there a simple way, preferably multiplataform (or linux), of
generating sinusoidal/square waves sound in python?

Have a look at the wave module, available under Windows and Linux,
which operates on .WAV files. The following snippet might get you going:

#!/usr/bin/python
import math, wave, struct

def signal(t, freq):
return math.sin(2.0*math.pi*freq*t)

wout = wave.open("sample.wav", "wb")
nchan = 1
sampwidth = 2
framerate = 8000
nframes = 7 * framerate
comptype = "NONE"
compname = "no compression"

wout.setparams((nchan, sampwidth, framerate, nframes, comptype, compname))

ts = 1.0 / framerate
t = 0.0
n = 0
data = []
vals = []
while n < nframes:
vals.append(signal(t, 517.0))
n = n + 1
t = t + ts

mx = max((abs(x) for x in vals))
vals = [ x/mx for x in vals ]
data = ""
for v in vals:
data = data + struct.pack("<h", int(v*32766.0))
wout.writeframes(data)
wout.close()

Alternatively you might just generate (t,signal) samples, write them to
a file and convert them using "sox" (under Linux, might also be available
under Windows) to another format.

HTH
Martin

K

#### K Richard Pixley

Hi,
Sorry if this is a FAQ, but I have googled and didn't find any

Is there a simple way, preferably multiplataform (or linux), of
generating sinusoidal/square waves sound in python?

I just posted on this elsewhere. Look for a thread titled: "Which
library for audio playback ?"

--rich

P

#### Paulo da Silva

Em 30-12-2011 10:05, Dave Angel escreveu:
If you're willing to be Linux-only, then I believe you can do it without
any extra libraries.

You build up a string (8 bit char, on Python 2.x) of samples, and write
it to "/dev/audio". When i experimented, I was only interested in a
few seconds, so a single write was all I needed.

Note that the samples are 8 bits, and they are offset by 128. So a zero
signal would be a string of 128 values. A very quiet square wave might
be a bunch of 126, followed by a bunch of 130. and so on. And the
loudest might be a bunch of 2's followed by a bunch of 253's.

You'll have to experiment with data rate; The data is sent out at a
constant rate from your string, but I don't know what that rate is.
This sounds nice, but then is 8 bits the limit for /dev/audio? What
about stereo? I don't need this one ... just for curiosity.
Thanks.

P

#### Paulo da Silva

Em 30-12-2011 11:23, mblume escreveu:
Am Fri, 30 Dec 2011 07:17:13 +0000 schrieb Paulo da Silva: ....

Alternatively you might just generate (t,signal) samples, write them to
a file and convert them using "sox" (under Linux, might also be available
under Windows) to another format.
As much as I could understand at a 1st look you are writing to a wav
file and then play the file.
It would be nice if I could play directly the samples.
Anyway I'll take a look at the wave module.
Thanks

P

#### Paulo da Silva

Em 31-12-2011 01:19, K Richard Pixley escreveu:
I just posted on this elsewhere. Look for a thread titled: "Which
library for audio playback ?"

--rich

Thank you. I have just seen it using google and saved the bookmark of

D

#### Dave Angel

Em 30-12-2011 10:05, Dave Angel escreveu:
This sounds nice, but then is 8 bits the limit for /dev/audio? What
about stereo? I don't need this one ... just for curiosity.
Thanks.
I don't even remember where I got the information, but it sufficed for
my needs. I wanted to be able to generate arbitrary tones at a high
volume, bypassing any volume control system settings. I assume there's
some way (ioctl ?) to tell the device to interpret differently. It's
even possible that it's already stereo (left/right samples stored in
adjacent 16bit locations -- it wouldn't change the effect I hear, except
for the frequency being cut in half.

Interesting link from1991, it's from Guido, but doesn't mention Python
http://wiretap.area.com/Gopher/Library/Techdoc/Misc/audiofor.faq
Also, a lot has changed since then.

Now I wonder whether I should be sending u-law values, rather than
linear ones. I'm generating sine waves, and they don't really sound
flutelike.

http://www.faqs.org/docs/Linux-HOWTO/Sound-HOWTO.html

I suspect that my approach will simply use the latest setup values (eg.
sampling rate) and thus runs the risk of sometimes not working. That
hasn't been my experience, The only problem I see is that sometimes the
device is "busy". When that happens, other programs don't seem to work
either. I need to find the rogue process which is hogging the device,
using fuser.

P

#### Paulo da Silva

Em 30-12-2011 07:17, Paulo da Silva escreveu:
Hi,
Sorry if this is a FAQ, but I have googled and didn't find any

Is there a simple way, preferably multiplataform (or linux), of
generating sinusoidal/square waves sound in python?

Thank you very much to all who responded.
There is enough material here to spend some time searching for the best
solution for me.
In the meanwhile I also found http://www.speech.kth.se/snack.
May be it could also be useful.

Thank you.

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