code: func (s *stream) Read(buf []byte) (int, error) {
  	if len(s.remaining) > 0 {
  		n := copy(buf, s.remaining)
  		s.remaining = s.remaining[n:]
  		return n, nil
  	}
  
  	var origBuf []byte
  	if len(buf)%4 > 0 {
  		origBuf = buf
  		buf = make([]byte, len(origBuf)+4-len(origBuf)%4)
  	}
  
  	const length = int64(sampleRate / frequency)
  	p := s.position / 4
  	for i := 0; i < len(buf)/4; i++ {
  		const max = 32767
  		b := int16(math.Sin(2*math.Pi*float64(p)/float64(length)) * max)
  		buf[4*i] = byte(b)
  		buf[4*i+1] = byte(b >> 8)
  		buf[4*i+2] = byte(b)
  		buf[4*i+3] = byte(b >> 8)
  		p++
  	}
  
  	s.position += int64(len(buf))
  	s.position %= length * 4
  
  	if origBuf != nil {
  		n := copy(origBuf, buf)
  		s.remaining = buf[n:]
  		return n, nil
  	}
  	return len(buf), nil
  }
docs: // Read is io.Reader's Read.
  //
  // Read fills the data with sine wave samples.