# FMOD\_ERR\_INVALID\_PARAM when adding DSP to ChannelGroup

**URL:** https://qa.fmod.com/t/fmod-err-invalid-param-when-adding-dsp-to-channelgroup/13939
**Category:** FMOD Engine
**Created:** [June 12, 2018, 5:21pm UTC](https://qa.fmod.com/t/fmod-err-invalid-param-when-adding-dsp-to-channelgroup/13939 "2018-06-12T17:21:18Z")
**Posts on this page:** 2
**Page:** 1

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### Author: ![Abvadabra](https://yyz2.discourse-cdn.com/flex036/user_avatar/qa.fmod.com/abvadabra/32/2061_2.png) [@Abvadabra](https://qa.fmod.com/u/Abvadabra)
#### Post date: [June 12, 2018, 5:21pm UTC](https://qa.fmod.com/t/fmod-err-invalid-param-when-adding-dsp-to-channelgroup/13939/1 "2018-06-12T17:21:18Z")

</div>

I keep getting FMOD\_ERR\_INVALID\_PARAM when trying to add DSP of type FMOD\_DSP\_TYPE\_LOWPASS to custom ChannelGroup.  
I double checked that the DSP is created successfully and ChannelGroup is initialized properly. What else could cause this error?

```
FMOD::ChannelGroup master = 0;
system->getMasterChannelGroup(&master);

FMOD::ChannelGroup worldSfxGroup = 0;
CHECK_ERR(system->createChannelGroup("World", &worldSfxGroup));
master->addGroup(worldSfxGroup);

FMOD::DSP lpf;
CHECK_ERR(system->createDSPByType(FMOD_DSP_TYPE_LOWPASS));
CHECK_ERR(worldSfxGroup->addDSP(2, lpf)); //FMOD_ERR_INVALID_PARAM on this line
```

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<div class="post-metadata">

### Author: ![cameron-fmod](https://yyz2.discourse-cdn.com/flex036/user_avatar/qa.fmod.com/cameron-fmod/32/261_2.png) [@cameron-fmod](https://qa.fmod.com/u/cameron-fmod)
#### Post date: [June 14, 2018, 11:52pm UTC](https://qa.fmod.com/t/fmod-err-invalid-param-when-adding-dsp-to-channelgroup/13939/2 "2018-06-14T23:52:59Z")

</div>

The first parameter of ChannelGroup::addDSP() is a FMOD\_CHANNELCONTROL\_DSP\_INDEX and ‘2’ is not a valid value.

[https://fmod.com/resources/documentation-api?page=content/generated/FMOD\_CHANNELCONTROL\_DSP\_INDEX.html](https://fmod.com/resources/documentation-api?page=content/generated/FMOD_CHANNELCONTROL_DSP_INDEX.html)