simple explanation please

pilot0315

QSIN(length, angle, twopi) : y Rotate (length,0) by (angle / twopi) * 2Pi and return y. Use 0 for twopi = $1_0000_0000. Twopi is unsigned.
QCOS(length, angle, twopi) : x Rotate (length,0) by (angle / twopi) * 2Pi and return x. Use 0 for twopi = $1_0000_0000. Twopi is unsigned.

I was looking at this code so as to attempt to out put three different pulsed sounds that increase and decrease in loudness. Need three different frequencies. Found this code but do not understand the twopi. Can any one reference me to some simple explanations please.
Thank you in advance.
Plus some relatively simple example code with good comments.
Thanks

cgracey

Twopi is just the value that represents an entire circumference. If it is 4, then angles 0..3 would be 0, 90, 180, and 270 degrees.

JRoark

@cgracey said:
Twopi is just the value that represents an entire circumference. If it is 4, then angles 0..3 would be 0, 90, 180, and 270 degrees.

Chip: Its actually a (badly named) function in this case instead of a value (per that PDF). The twopi function uses two sins 90 degrees out of phase in cartesian space to create a circle upon which the graph data is imposed. I think.

cgracey

Oh, okay. I was just thinking about the QSIN and QCOS methods in Spin2, and their third argument called 'twopi'. I hadn't even looked at the pdf because I didn't think it was necessary.

Ariba

Here is an example in Spin2 to generate an audio sine frequency:
https://forums.parallax.com/discussion/comment/1496551/#Comment_1496551

You can do this 3 times in the loop to generate 3 frequencies. To modulate the amplitude make the $7FFF a variable and change it from 0 to $7FFF and back to 0 to increase / decrease the loudness.

Andy

Ariba

The example modified for two frequencies and the amplitude modulated by a triangle waveform:

CON
  _clkfreq = 180_000_000

  smprate  = 44100
  sinfreq1 = 440
  sinfreq2 = 734
  dacpin1  = 36
  dacpin2  = 37
  lforate  = 3

VAR
  long  vol, lfo

pub sine_out() | smp, phs1, phs2
  pinstart(dacpin1, P_DAC_DITHER_RND | P_DAC_600R_2V | P_OE, clkfreq/smprate, 0)  'smartpin DAC 16bits
  pinstart(dacpin2, P_DAC_DITHER_RND | P_DAC_600R_2V | P_OE, clkfreq/smprate, 0)
  repeat
     phs1 += sinfreq1 FRAC smprate             'rotate phase by one step angle for sine freq
     _,smp := polxy(vol, phs1)                 'cordic sine with rotating phase and modulated volume
     wypin(dacpin1, smp+$8000)                 'write sine sample to dac

     phs2 += sinfreq2 FRAC smprate
     _,smp := polxy(vol, phs2)                 'the same for the second frequency
     wypin(dacpin2, smp+$8000)

     repeat until pinread(dacpin1)             'wait for dac sample period

     lfo := (lfo + lforate) & $FFFF            'low freq. Oscillator (sawtooth)
     vol := abs(lfo - $8000)                   'saw to triangle = up/down ramp

Andy

ersmith

Just for clarity: the "twopi" variable mentioned in the QSIN and QCOS documentation has nothing at all to do with the "twopi" function described in your linked PDF file. They just happen to share a name.

pilot0315

Thanks to all.
@ersmith
Thanks for the explanation.
@Ariba
I will try your code.
Thanks