Sine wave?

[Bengt Richter]

On Sun, 22 Dec 2002 13:42:19 -0500, "EC" <vitamonkey at home.com> wrote:

>Ive been banging my head against the wall for the past few days trying to
>generate a sine wave... My math skills arent the best, I'll admit, and I
>think I'm going crosseyed trying to understand this... I *think* the
>following code should work but it outputs some really weird stuff.  I'm
>sorta new so please help if you can! Thank you
>
>Eric
>
>#-------------------------------------------
>import math
>import wave
>import string
>
>pi = math.pi
>sin = math.sin
>cos = math.cos
>
>#init output and related vars
>sr = 44100
>Outfile = wave.open("outfile.wav", "w")
>Outfile.setnchannels(1)
>Outfile.setsampwidth(4)
>Outfile.setframerate(sr)
>Outfile.setcomptype("NONE", "Uncompressed")
>Outtemp = []
>Outstr = ""
>
>def get_phase(curphs, freq):
>    phinc = (freq*1.0000/sr*1.0000)*360
>    phase = curphs + phinc
>    if phase >= 360:
>        phase -= 360
>    elif phase < 0:
>        phase += 360
>    return phase
>
>def gen_wav(sec, freq, ampcent):
>    numsamp = sec*sr
>    amp = (ampcent*1.0000/100)*32767
>    i = 0
>    temp = []
>    t = 0
>    curphase = 0
>    while i < numsamp:
>        curphase = get_phase(curphase, freq)
>        t = int(round(amp*sin(2*pi*curphase)))
>        temp.append(t)
>        i+=1
>    return temp
>
>Outtemp = gen_wav(.01, 440, 75)
>
>Outstr = string.join(map(str, Outtemp), ",")
>print Outstr
>Outfile.writeframes(Outstr)
>Outfile.close()
>
Try this ( just run  python sinewave.py and it should generate 2 seconds
of 2khz at 75% amplitude that you can listen to with media player.
Also will plot the first 34 samples on console screen, self-scaling
when it exceeds the display region (right away here). See after this.
My media player didn't like 4-byte samples, so that was changed, among
other things ;-)

#--< sinewave. py >-------------------------------------------
import math
import wave
import array

pi = math.pi
twopi = 2.0*pi
sin = math.sin
cos = math.cos

#init output and related vars
samplesPerSecond = 44100
Outfile = wave.open("outfile.wav", "w")
Outfile.setnchannels(1)
Outfile.setsampwidth(2) # 2 bytes for 32767 amplitude
Outfile.setframerate(samplesPerSecond)
Outfile.setcomptype("NONE", "Uncompressed")

def gen_wav(seconds, frequency, amplitudePercentOfMax):
    # calculate frequency as cycles/sample
    cyclesPerSample = float(frequency)/samplesPerSecond
    numberOfSamples = int(seconds*samplesPerSecond)
    maxAmplitude = (amplitudePercentOfMax/100.)*32767
    sampleArray = array.array('h')

    for nSamples in xrange(numberOfSamples):
        cycles = nSamples*cyclesPerSample
        cycles -= int(cycles) # makes 0.0<=cycles<1.0
        sampleValue = int(round(maxAmplitude*sin(twopi*cycles))) # round 
        sampleArray.append(sampleValue)
    return sampleArray

if __name__ == '__main__':
    
    #Outtemp = gen_wav(.01, 440, 75)
    # generate .001 sec = 44.1 samples & 2 cycles with 20 amplitude
    #sampleArray = gen_wav(.00075, 2000, (20./32767.)*100)
    sampleArray = gen_wav(2, 2000, 75)

    # print first 34 samples as selfscaling ascii plot
    grid = list(' |%19s|%19s|' %('',''))
    scale = 1.0; maximumMagnitude = 20
    for i in range(min(34,len(sampleArray))):
        sample= sampleArray[i]
        if abs(sample)>maximumMagnitude:
            maximumMagnitude=abs(sample)
            scale = 20./maximumMagnitude
        x= int(round(sampleArray[i]*scale))+21
        print ''.join(grid[:x]+['*']+grid[x+1:])
    
    Outfile.writeframes(sampleArray.tostring())
    Outfile.close()
#-------------------------------------------------------------

Output from above:

[14:27] C:\pywk\clp>python sinewave.py
 |                   *                   |
 |                   |                   *
 |                   |                   *
 |                   |                   *
 |                   |                   *
 |                   |                   *
 |                   |                   *
 |                   |                 * |
 |                   |              *    |
 |                   |          *        |
 |                   |     *             |
 |                   *                   |
 |             *     |                   |
 |        *          |                   |
 |    *              |                   |
 | *                 |                   |
 *                   |                   |
 *                   |                   |
 | *                 |                   |
 |    *              |                   |
 |        *          |                   |
 |             *     |                   |
 |                   *                   |
 |                   |    *              |
 |                   |          *        |
 |                   |              *    |
 |                   |                 * |
 |                   |                   *
 |                   |                   *
 |                   |                 * |
 |                   |              *    |
 |                   |          *        |
 |                   |     *             |
 |                   *                   |

Regards,
Bengt Richter