# SIMD Register Tutorial Multichannel

**URL:** <https://forum.juce.com/t/simd-register-tutorial-multichannel/53326>\
**Category:** General JUCE discussion\
**Created:** [October 12, 2022, 1:59pm UTC](https://forum.juce.com/t/simd-register-tutorial-multichannel/53326 "2022-10-12T13:59:52Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![rollo](https://avatars.discourse-cdn.com/v4/letter/r/e9bcb4/32.png) [@rollo](https://forum.juce.com/u/rollo)\
**Post date:** [October 12, 2022, 1:59pm UTC](https://forum.juce.com/t/simd-register-tutorial-multichannel/53326/1 "2022-10-12T13:59:52Z")

</div>

Hi all, I tried to follow the SIMD Tutorial ([JUCE: Tutorial: Optimisation using the SIMDRegister class](https://docs.juce.com/master/tutorial_simd_register_optimisation.html))

I can’t figure out how to use it for more channels than the register size.  
I’m on an M1 Mac with supports a 128bit registry, so I can fit 4 floats in there.  
For simplicity I’d process only multiples of 4, so let’s say 12 channels.

To test the multichannel stuff, i created an AudioBuffer with 12 channels and copied sample data to it in `getNextAudioBlock( const juce::AudioSourceChannelInfo& bufferToFill)`

Should i then in the SIMDTutorialFilter create multiple iir filters?  
`std::vector<std::unique_ptr<dsp::IIR::Filter<dsp::SIMDRegister<float>>>> iir;`

Then in process() align and interleave them and call iir-\>process on all of them?

```auto
  for (int i = 0; i < numChannels / registerSize; ++i)
        {
            auto subInputBlock = inputBlock.getSubsetChannelBlock (i * registerSize, registerSize);
            
            auto inChannels = prepareChannelPointers(subInputBlock);
            
            using Format = AudioData::Format<AudioData::Float32, AudioData::NativeEndian>;
            AudioData::interleaveSamples(AudioData::NonInterleavedSource<Format> { inChannels.data(), registerSize },
                                         AudioData::InterleavedDest<Format> {toBasePointer(interleaved.getChannelPointer(0)), registerSize},
                                         numSamples);
            
            iir[i]->process(dsp::ProcessContextReplacing<dsp::SIMDRegister<float>>(interleaved));
            
            auto outputBlock = context.getOutputBlock();
            auto subOutputBlock = outputBlock.getSubsetChannelBlock (i * registerSize, registerSize);

            auto outChannels = prepareChannelPointers (subOutputBlock);
            
            AudioData::deinterleaveSamples(AudioData::InterleavedSource<Format> {toBasePointer(interleaved.getChannelPointer(0)), registerSize},
                                           AudioData::NonInterleavedDest<Format> {outChannels.data(), registerSize}, numSamples);
        }

```

It feels like the wrong thing to do and also introduces crackling on all but the first 4 channels 😕  
Any better solutions?  
thanks! ❤