# dsp::Oversampling setup

**URL:** <https://forum.juce.com/t/dsp-oversampling-setup/46896>\
**Category:** General JUCE discussion\
**Created:** [July 12, 2021, 1:32am UTC](https://forum.juce.com/t/dsp-oversampling-setup/46896 "2021-07-12T01:32:53Z")\
**Posts on this page:** 20\
**Page:** 1

<div class="post-metadata">

**Author:** ![baintonaj](https://avatars.discourse-cdn.com/v4/letter/b/22d042/32.png) [@baintonaj](https://forum.juce.com/u/baintonaj)\
**Post date:** [July 12, 2021, 1:32am UTC](https://forum.juce.com/t/dsp-oversampling-setup/46896/1 "2021-07-12T01:32:53Z")

</div>

Hi, I am having trouble configuring dsp::Oversampling in my plug-in. Here’s what I have:

PluginProcessor.h

```
Private:
juce::dsp::Oversampling<float> oversampler;

```

PluginProcessor.cpp

```
//Constructor
oversampler(1, 3, juce::dsp::Oversampling<float>::FilterType::filterHalfBandFIREquiripple, true )

//Prepare to Play
oversampler.setUsingIntegerLatency(true);
oversampler.reset();

//Process Block
oversampler.initProcessing(buffer.getNumSamples());

oversampler.addOversamplingStage(juce::dsp::Oversampling<float>::FilterType::filterHalfBandFIREquiripple, 0.1f, -18.0f, 0.1f, -96.0f);
    
auto returnBlock = oversampler.processSamplesUp(juce::dsp::AudioBlock<float>(buffer));

```

The error I am receiving in Logic Pro is about not having the right number of channels in these lines:

```
//juce_Oversampling.cpp::159
void processSamplesUp ( const AudioBlock< const SampleType>& inputBlock) override
{
    jassert (inputBlock.getNumChannels() <= static_cast <size_t> (ParentType::buffer.getNumChannels()));

//juce_AudioSampleBuffer.h:322
Type* getWritePointer (int channelNumber) noexcept
{
    jassert (isPositiveAndBelow (channelNumber, numChannels));

```

I think this has something to do with the buffer translating to .processSamplesUp().

Any idea where I am going wrong?

Thank you,  
Andy

---

<div class="post-metadata">

**Author:** ![reuk](https://sea2.discourse-cdn.com/flex026/user_avatar/forum.juce.com/reuk/32/21494_2.png) [@reuk](https://forum.juce.com/u/reuk)\
**Post date:** [July 12, 2021, 6:46am UTC](https://forum.juce.com/t/dsp-oversampling-setup/46896/2 "2021-07-12T06:46:02Z")

</div>

It looks like your `Oversampling` instance is only being prepared to work with a single channel (the first constructor argument). If your plugin accepts multiple channels, you must initialise the Oversampling instance with the same number of channels.

There are a few other issues in the snippet you posted that might prevent the Oversampling class from working as expected: Normally, `initProcessing` would be called from `prepareToPlay`. Calling it in each block may cause issues. Also, calling `addOversamplingStage` inside `processBlock` will add a new stage on each audio callback, which is unlikely to be what you want. Finally, you need to call `oversampler.processSamplesDown (outputBlock)` after doing your processing on the `returnBlock` in order to return the block to the host’s sampling rate.

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<div class="post-metadata">

**Author:** ![baintonaj](https://avatars.discourse-cdn.com/v4/letter/b/22d042/32.png) [@baintonaj](https://forum.juce.com/u/baintonaj)\
**Post date:** [July 12, 2021, 8:30am UTC](https://forum.juce.com/t/dsp-oversampling-setup/46896/3 "2021-07-12T08:30:54Z")

</div>

Thank you for your help! I switched the channel number to 2 from 1 and Logic still gives errors on those channel-based jassert lines. Is there something else I am missing?

I appreciate your help with the organization!

---

<div class="post-metadata">

**Author:** ![reuk](https://sea2.discourse-cdn.com/flex026/user_avatar/forum.juce.com/reuk/32/21494_2.png) [@reuk](https://forum.juce.com/u/reuk)\
**Post date:** [July 12, 2021, 9:01am UTC](https://forum.juce.com/t/dsp-oversampling-setup/46896/4 "2021-07-12T09:01:50Z")

</div>

It sounds like the audio buffer being passed into `processSamplesUp` still has more channels than the oversampler is expecting. When you hit the assertion in `processSamplesUp`, you should be able to see the number of channels in the `inputBlock` in your debugger. (You could also add a `DBG (inputBlock.getNumChannels())` statement to print the number of channels in the block).

If your plugin only supports certain channel counts, you should override `isBusesLayoutSupported` in your `AudioProcessor` to prevent the plugin from being instantiated with an unsupported channel layout.

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<div class="post-metadata">

**Author:** ![baintonaj](https://avatars.discourse-cdn.com/v4/letter/b/22d042/32.png) [@baintonaj](https://forum.juce.com/u/baintonaj)\
**Post date:** [July 12, 2021, 10:39pm UTC](https://forum.juce.com/t/dsp-oversampling-setup/46896/5 "2021-07-12T22:39:44Z")

</div>

I’ve configured `isBussesLayoutSupported` to only support stereo processing, and have configured my oversampler in PluginProcessor.h to look like this. The jasserts still come up. The channels of the inputBlock and the buffer read 2 and 2. Is there something I am missing?

```
juce::dsp::Oversampling<float> oversampler { 2, 1, juce::dsp::Oversampling<float>::FilterType::filterHalfBandFIREquiripple, true };
```

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<div class="post-metadata">

**Author:** ![reuk](https://sea2.discourse-cdn.com/flex026/user_avatar/forum.juce.com/reuk/32/21494_2.png) [@reuk](https://forum.juce.com/u/reuk)\
**Post date:** [July 13, 2021, 7:43am UTC](https://forum.juce.com/t/dsp-oversampling-setup/46896/6 "2021-07-13T07:43:53Z")

</div>

When you hit the first assertion, try checking all of the values involved to work out why the assertion is firing. Then, you should be able to look up the call stack to find out where the incorrect value is coming from.

Are you sure that you’re initialising the oversampler correctly? If the input block _definitely_ has only two channels, you should check `ParentType::buffer.getNumChannels()` to make sure that the oversampler is prepared to process that many channels.

---

<div class="post-metadata">

**Author:** ![baintonaj](https://avatars.discourse-cdn.com/v4/letter/b/22d042/32.png) [@baintonaj](https://forum.juce.com/u/baintonaj)\
**Post date:** [July 18, 2021, 9:16pm UTC](https://forum.juce.com/t/dsp-oversampling-setup/46896/7 "2021-07-18T21:16:35Z")

</div>

Thank you for your help. How do I check the `ParentType::buffer.getNumChannels()`? I have done `oversampler.numChannels` and compared it to `buffer.getNumChannels()` and the two match in my `cout` statement. Even when I set the oversampler to `0` channels, I still get the flag in Logic that

> [@baintonaj](#):
>
> `jassert (inputBlock.getNumChannels() <= static_cast <size_t> (ParentType::buffer.getNumChannels()));`

Thanks!

---

<div class="post-metadata">

**Author:** ![reuk](https://sea2.discourse-cdn.com/flex026/user_avatar/forum.juce.com/reuk/32/21494_2.png) [@reuk](https://forum.juce.com/u/reuk)\
**Post date:** [July 18, 2021, 9:52pm UTC](https://forum.juce.com/t/dsp-oversampling-setup/46896/8 "2021-07-18T21:52:08Z")

</div>

> [@baintonaj](#):
>
> How do I check the `ParentType::buffer.getNumChannels()` ?

You can either look at the number of channels in the `buffer` member using a debugger, or you could add a line like this to the oversampler implementation:

```cpp
DBG ("input block: " << inputBlock.getNumChannels() << " parent buffer: " << ParentType::buffer.getNumChannels());

```

---

<div class="post-metadata">

**Author:** ![baintonaj](https://avatars.discourse-cdn.com/v4/letter/b/22d042/32.png) [@baintonaj](https://forum.juce.com/u/baintonaj)\
**Post date:** [July 18, 2021, 10:01pm UTC](https://forum.juce.com/t/dsp-oversampling-setup/46896/9 "2021-07-18T22:01:34Z")

</div>

OK! So it says the parent buffer is 0, and the input buffer is 2. How do I adjust the parent buffer? I have my set up to look like this:

```
//Initialization
 oversampler( 2, 1, juce::dsp::Oversampling< float >::FilterType::filterHalfBandFIREquiripple, true, true )

//Prepare to Play
oversampler.numChannels = getTotalNumInputChannels();
oversampler.factorOversampling = 1;
oversampler.initProcessing(samplesPerBlock);
oversampler.setUsingIntegerLatency(true);
oversampler.reset();

oversampler.clearOversamplingStages();    
oversampler.addOversamplingStage(juce::dsp::Oversampling<float>::FilterType::filterHalfBandFIREquiripple, 0.05f, -90.0f, 0.05f, -90.0f);

setLatencySamples(oversampler.getLatencyInSamples());
```

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<div class="post-metadata">

**Author:** ![reuk](https://sea2.discourse-cdn.com/flex026/user_avatar/forum.juce.com/reuk/32/21494_2.png) [@reuk](https://forum.juce.com/u/reuk)\
**Post date:** [July 18, 2021, 10:43pm UTC](https://forum.juce.com/t/dsp-oversampling-setup/46896/10 "2021-07-18T22:43:09Z")

</div>

What is the value of `getTotalNumInputChannels()` in `prepareToPlay()`?

---

<div class="post-metadata">

**Author:** ![baintonaj](https://avatars.discourse-cdn.com/v4/letter/b/22d042/32.png) [@baintonaj](https://forum.juce.com/u/baintonaj)\
**Post date:** [July 19, 2021, 1:47am UTC](https://forum.juce.com/t/dsp-oversampling-setup/46896/11 "2021-07-19T01:47:30Z")

</div>

It says 2!

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<div class="post-metadata">

**Author:** ![karota](https://sea2.discourse-cdn.com/flex026/user_avatar/forum.juce.com/karota/32/8238_2.png) [@karota](https://forum.juce.com/u/karota)\
**Post date:** [July 19, 2021, 7:38am UTC](https://forum.juce.com/t/dsp-oversampling-setup/46896/12 "2021-07-19T07:38:42Z")

</div>

Hi @baintonaj !

Might I ask you where you initialize your oversampler? Because it does not have a default constructor and so you should initialize it in the initializer list of your PluginProcessor constructor.

By the way, I used the oversampler for one of my plugins and I never got that issue. I can send you my own implementation if you would like to see: [CutTheMooog/LockWavefolder.cpp at develop · maurizdeb/CutTheMooog · GitHub](https://github.com/maurizdeb/CutTheMooog/blob/develop/Source/Processors/LockWavefolder.cpp)

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<div class="post-metadata">

**Author:** ![reuk](https://sea2.discourse-cdn.com/flex026/user_avatar/forum.juce.com/reuk/32/21494_2.png) [@reuk](https://forum.juce.com/u/reuk)\
**Post date:** [July 19, 2021, 8:52am UTC](https://forum.juce.com/t/dsp-oversampling-setup/46896/13 "2021-07-19T08:52:37Z")

</div>

I think the problem is that the number of channels in the oversampling stage’s buffer is only set during `initProcessing`. Moving the call to `initProcessing` after the call to `addOversamplingStage` should resolve the issue.

---

<div class="post-metadata">

**Author:** ![baintonaj](https://avatars.discourse-cdn.com/v4/letter/b/22d042/32.png) [@baintonaj](https://forum.juce.com/u/baintonaj)\
**Post date:** [July 19, 2021, 6:47pm UTC](https://forum.juce.com/t/dsp-oversampling-setup/46896/14 "2021-07-19T18:47:05Z")

</div>

Hey! This worked! Thank you so much!

I am now having an issue with `processSamplesDown()` where line 202 in juce\_Oversampling.cpp throws the following error, even thought `outputBlock.getNumSamples() * ParentType::factor == 4096` and `ParentType::buffer.getNumSamples() == 32768`. Is the second number higher than I should be expecting for a buffer? Thank you!

```
jassert (outputBlock.getNumSamples() * ParentType::factor <= static_cast<size_t> (ParentType::buffer.getNumSamples()));
```

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<div class="post-metadata">

**Author:** ![baintonaj](https://avatars.discourse-cdn.com/v4/letter/b/22d042/32.png) [@baintonaj](https://forum.juce.com/u/baintonaj)\
**Post date:** [July 19, 2021, 6:50pm UTC](https://forum.juce.com/t/dsp-oversampling-setup/46896/15 "2021-07-19T18:50:51Z")

</div>

Hi! I initialized the oversampler in the top most part of the default JUCE constructor. I think that is the right place. Thank you for your example! 🙂

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<div class="post-metadata">

**Author:** ![reuk](https://sea2.discourse-cdn.com/flex026/user_avatar/forum.juce.com/reuk/32/21494_2.png) [@reuk](https://forum.juce.com/u/reuk)\
**Post date:** [July 20, 2021, 8:58am UTC](https://forum.juce.com/t/dsp-oversampling-setup/46896/16 "2021-07-20T08:58:45Z")

</div>

I can’t reproduce this problem, so I’m not sure exactly what’s going on. It’s easier for other people to help if you provide a small program which exhibits the problem.

I don’t think that assertion would fire if the left-hand of the `<=` is really smaller than the right-hand side. I’d recommend adding some logging to make absolutely sure of the values involved in the assertion. If you put the logging directly _before_ the assertion, then at the point that you hit the assertion, you’ll be able to see the values involved in the console window.

It looks a bit suspicious that you’re writing to the `factorOversampling` data member. Modifying this member directly may break the invariants of the Oversampling instance. I’d recommend removing all writes to `factorOversampling` and checking whether that resolves your problem.

---

<div class="post-metadata">

**Author:** ![karota](https://sea2.discourse-cdn.com/flex026/user_avatar/forum.juce.com/karota/32/8238_2.png) [@karota](https://forum.juce.com/u/karota)\
**Post date:** [July 20, 2021, 9:47am UTC](https://forum.juce.com/t/dsp-oversampling-setup/46896/17 "2021-07-20T09:47:21Z")

</div>

Might I see how and where you call processSamplesUp() and processSamplesDown()?

---

<div class="post-metadata">

**Author:** ![baintonaj](https://avatars.discourse-cdn.com/v4/letter/b/22d042/32.png) [@baintonaj](https://forum.juce.com/u/baintonaj)\
**Post date:** [July 22, 2021, 9:37pm UTC](https://forum.juce.com/t/dsp-oversampling-setup/46896/18 "2021-07-22T21:37:17Z")

</div>

Here’s how I am calling the two functions now. I am not getting any logical errors in Logic, but I am not seeing the effects of the oversampling filter in DDMF’s PluginDoctor.

```
auto returnBlock = oversampler.processSamplesUp(buffer);
juce::AudioBuffer<float> buffer2;
returnBlock.copyTo(buffer2);

//Processing using buffer2

juce::dsp::AudioBlock<float> outputBlock;
outputBlock.copyFrom(buffer2);
oversampler.processSamplesDown(outputBlock);
for (auto i = totalNumInputChannels; i < totalNumOutputChannels; ++i)
    buffer.clear (i, 0, buffer.getNumSamples());
outputBlock.copyTo(buffer);
```

---

<div class="post-metadata">

**Author:** ![karota](https://sea2.discourse-cdn.com/flex026/user_avatar/forum.juce.com/karota/32/8238_2.png) [@karota](https://forum.juce.com/u/karota)\
**Post date:** [July 22, 2021, 10:34pm UTC](https://forum.juce.com/t/dsp-oversampling-setup/46896/19 "2021-07-22T22:34:41Z")

</div>

Hi @baintonaj !

So first of all, why are u calling always audioblock.copyTo(audioBuffer) ?

> [@baintonaj](#):
>
> ```auto
> juce::AudioBuffer<float> buffer2;
> returnBlock.copyTo(buffer2);
> 
> ```

After the upsampling process you can use directly the returnBlock. That audioblock already contains a reference to the upsampled buffer! Moreover, you can get the audiosamples directly by calling returnBlock.getChannelPointer(channel)[numSample].

I think that creating a new buffer and calling copyTo function, could allocate new memory in the buffer2 (but I am not sure if this happens, I’ve never used copyTo() ) . And allocating new memory on the audio thread is always a not-safe operation 🙂

What you could do is simply

```auto
dsp::AudioBlock<float> inputBlock (buffer);
auto returnBlock = oversampler.processSamplesUp(inputBlock);

// Processing using returnBlock

oversampler.processSamplesDown(inputBlock);

// Continue processing using inputBlock

```

---

<div class="post-metadata">

**Author:** ![baintonaj](https://avatars.discourse-cdn.com/v4/letter/b/22d042/32.png) [@baintonaj](https://forum.juce.com/u/baintonaj)\
**Post date:** [July 23, 2021, 1:47am UTC](https://forum.juce.com/t/dsp-oversampling-setup/46896/20 "2021-07-23T01:47:12Z")

</div>

Hey! Thank you for your help! I got it to work! I didn’t realize you could use `getChannelPointer()` in an audio block like `getWritePointer()` in a buffer. That solved all my problems!