Degenerator DIY Sampler/Synthesizer (Tubeohm)

//*************************************************************************
// OscRender: VOWEL
//*************************************************************************
void OscRender_Vowel(uint8_t osc_nr)
{
    uint8_t block_size = 40;
    uint8_t parameter;
    uint8_t *buffer;
    uint8_t ix = 0;
    
    if (osc_nr == 0)
    {
        parameter = Osc.prm[0];
        if (Voice.buffer_nr == 0)
        {
            buffer = Voice.Buffer2a;
        }
        else {buffer = Voice.Buffer1a;}
    }
    else
    {
        parameter = Osc.prm[1];
        if (Voice.buffer_nr == 0)
        {
            buffer = Voice.Buffer2b;
        }
        else {buffer = Voice.Buffer1b;}
    }
    
    Osc.vw_update = (Osc.vw_update + 1) & 3;
    if (!Osc.vw_update) {
        uint8_t offset_1 = U8ShiftRight4(parameter);
        offset_1 = U8U8Mul(offset_1, 7);
        uint8_t offset_2 = offset_1 + 7;
        uint8_t balance = parameter & 15;
    
    // Interpolate formant frequencies.
    for (uint8_t i = 0; i < 3; ++i) {
        Osc.vw_formant_increment[i] = U8U4MixU12(
        pgm_read_byte (&(wav_res_vowel_data[offset_1 + i])),
        pgm_read_byte (&(wav_res_vowel_data[offset_2 + i])),balance);
        Osc.vw_formant_increment[i] <<= 3;
    }
    
    // Interpolate formant amplitudes.
    for (uint8_t i = 0; i < 4; ++i) {
        uint8_t amplitude_a = pgm_read_byte (&(wav_res_vowel_data[offset_1 + 3 + i]));
        uint8_t amplitude_b = pgm_read_byte (&(wav_res_vowel_data[offset_2 + 3 + i]));
        Osc.vw_formant_amplitude[i] = U8U4MixU8(amplitude_a,amplitude_b, balance);
    }
    }   
 
    // sample loop --------------------------------------------------------
    do
    {
        Osc.phase[osc_nr] += Osc.phase_increment[osc_nr];
        
        uint16_t phase_integral = Osc.phase[osc_nr] >> 8;
        uint16_t phase_increment_integral = Osc.phase_increment[osc_nr] >> 8;
        int8_t result = 0;
        
        for (uint8_t i = 0; i < 3; ++i) {
            Osc.vw_formant_phase[i] += Osc.vw_formant_increment[i];
            result += pgm_read_byte (&((i == 2 ? wav_res_formant_square : wav_res_formant_sine)
            [(((Osc.vw_formant_phase[i] >> 8) & 0xf0) | Osc.vw_formant_amplitude[i])]));
        }
        result = S8U8MulShift8(result, ~ (phase_integral >> 8));
        phase_integral += phase_increment_integral;
        int16_t phase_noise = (int8_t)(Noise.data_rng_state << 8) * 1;// (int8_t)Osc.noise_modulation;
        if (phase_integral + phase_noise < phase_increment_integral) {
            Osc.vw_formant_phase[0] = 0;
            Osc.vw_formant_phase[1] = 0;
            Osc.vw_formant_phase[2] = 0;
        }
        uint8_t x = S16ClipS8(4 * result) + 128;
        
        // write sample in sound-buffer
        buffer[ix++] = x;
        buffer[ix++] = x;
        block_size--;       
        
    } while (--block_size);

}