[BR] Initial noise-burst in dsp::Convolution

General JUCE discussion
1

Something’s amiss with my convolver.
It’s producing a noise burst the first time it renders audio.

using namespace dsp;

struct Spatializer
{
    dsp::Convolution convolver;
    AudioBuffer<float> outBuf;

    Spatializer(int toneme) {
        std::ostringstream ss;
        ss << "ir_" << std::setw(2) << std::setfill('0') << toneme << "_wav";
        String resourceName = ss.str();

        int size = 0;
        const void* data = BinaryData::getNamedResource(resourceName.getCharPointer(), size);

        dsp::ProcessSpec spec;
        spec.sampleRate = 44100;
        spec.maximumBlockSize = 4096;
        spec.numChannels = 2;
        convolver.prepare(spec);

        convolver.loadImpulseResponse(
            data,
            (size_t)size,
            dsp::Convolution::Stereo::yes,
            dsp::Convolution::Trim::no,
            (size_t)0,  // size (0 is original size)
            dsp::Convolution::Normalise::no
        );
        //convolver.reset();
    }

    void setBufferSize(int nSamps) {
        outBuf.setSize(2, nSamps);
        //outBuf.clear();
    }

    auto getOutBlock() {
        return dsp::AudioBlock<float>(outBuf);
    }

    void feed(const dsp::AudioBlock<float> in_mono)
    {
        // const not needed
        const float* pointers[] = {
            in_mono.getChannelPointer(0),
            in_mono.getChannelPointer(0)
        };

        // float** works too
        AudioBlock<float>tmpBlk((float * const *)&pointers, 2, (int)in_mono.getNumSamples());

        auto outBlock = getOutBlock();

        juce::dsp::ProcessContextNonReplacing<float> ctx(tmpBlk, outBlock);
        convolver.process(ctx);
    }
};

Attempts to .reset the Convolution instance, and/or to initially .clear my wrapper’s output buffer (just in case convolver.process(ctx) might be internally adding to the output buffer, of which I see no evidence) both fail to shake it loose.

The issue is definitely in this Convolver object. If I remove it from the pipeline, I don’t get the noiseburst:

// works
auto& note = *notes[prefs.spiral_midi_lowest];
outBlock.getSingleChannelBlock(0).add(note.getOutBlock());

// fails
auto& note = *notes[prefs.spiral_midi_lowest];
auto& spatializer = *spatializers[prefs.spiral_midi_lowest];
spatializer.feed(note.getOutBlock());
outBlock.add(spatializer.getOutBlock());

What DOES work is to “warm it up” by feeding in a boatload of zeros initially:

    void audioDeviceAboutToStart (AudioIODevice* pDevice) override {
        int N = pDevice->getCurrentBufferSizeSamples();

        for(auto p : notes)
            p->setBufferSize(N);

        for(auto p : spatializers) {
            p->setBufferSize(N);

            // 🔴 I had to add all this
            auto buf = AudioBuffer<float>(1, N);
            buf.clear();
            auto blk = AudioBlock<float>(buf);
            for(int i=0; i<32; ++i)  // low numbers like 4, I still get some noiseburst
                p->feed(blk);
        }
    }

… but this is ugly and imprecise – how many zeros should I initially feed it?
One FFT frame’s worth? Without digging into the internals, no way to know.

Has anyone else encountered trouble with this component?
I suspect it may be failing to internally zero its own buffers.