# Connecting DSPs vs connecting ChannelGroups
**URL:** https://qa.fmod.com/t/connecting-dsps-vs-connecting-channelgroups/20477
**Category:** FMOD Engine
**Created:** [July 28, 2023, 2:47am UTC](https://qa.fmod.com/t/connecting-dsps-vs-connecting-channelgroups/20477 "2023-07-28T02:47:32Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@heavisideresearch](https://qa.fmod.com/u/heavisideresearch)
#### Post date: [July 28, 2023, 2:47am UTC](https://qa.fmod.com/t/connecting-dsps-vs-connecting-channelgroups/20477/1 "2023-07-28T02:47:32Z")
I’m trying to understand the the relationship between channels and DSPs. As far as I understand it:
1. At the lowest level, we’ve got a graph of `DSP`s
2. some linear groups of them (DSP Chains) are wrapped up in `Channels` or `ChannelGroup`s
What I don’t understand is if the `Channel` to `Channel` relationships are anything separate from the `DSP` to `DSP` relationships.
For example, I can create 2 channel groups:
```auto
FMOD.ChannelGroup cg1, cg2;
coreSystem.createChannelGroup("cg1", out cg1);
coreSystem.createChannelGroup("cg2", out cg2);
```
which creates this graph
If I connect `cg2` to `cg1`, like this:
```auto
FMOD.ChannelGroup cg1, cg2;
coreSystem.createChannelGroup("cg1", out cg1);
coreSystem.createChannelGroup("cg2", out cg2);
cg2.addGroup(cg1);
```
I get this graph:
So `cg1` was disconnected from the master group and connected to `cg2`. I can do seemingly the same thing by manipulating the DSPs:
```auto
FMOD.ChannelGroup cg1, cg2;
coreSystem.createChannelGroup("cg1", out cg1);
coreSystem.createChannelGroup("cg2", out cg2);
FMOD.DSP cg1_fader, cg2_fader;
cg1.getDSP(0, out cg1_fader);
cg2.getDSP(0, out cg2_fader);
cg1_fader.disconnectAll(true, true);
cg2_fader.addInput(cg1_fader);
```
Is this the same thing? One thing that’s confusing is that a `ChannelGroup` is only supposed to have 1 parent, but if you’re routing the DSPs there’s nothing stopping you from routing a `ChannelGroup`’s output fader to multiple places.
Maybe a more concise wording for my question is "Is the tree of `Channel`s and `ChannelGroup`s separate from the graph of `DSP`s?
---
### Author:  [@Leah\_FMOD](https://qa.fmod.com/u/Leah_FMOD)
#### Post date: [July 31, 2023, 6:53am UTC](https://qa.fmod.com/t/connecting-dsps-vs-connecting-channelgroups/20477/2 "2023-07-31T06:53:39Z")
> [@heavisideresearch](#):
>
> Maybe a more concise wording for my question is "Is the tree of `Channel`s and `ChannelGroup`s separate from the graph of `DSP`s?
Yes and no. There isn’t a 1-to-1 relationship between a DSP and a Channel/ChanneGroup. A DSP is a single DSP unit in the chain. A ChannelGroup is a higher level grouping of DSPs, that at minimum includes the Fader DSP you’re observing, but can also include DSPs for playing sounds or plugins, effect DSPs, and other Channels or ChannelGroups. Additionally, while the DSP graph can be manipulated such that a DSP interacts with the signal from multiple Channels, a DSP can only “belong” to a single Channel/ChannelGroup.
I hope that answers your question - feel free to ask if you’re still unclear on anything.
---
### Author:  [@heavisideresearch](https://qa.fmod.com/u/heavisideresearch)
#### Post date: [July 31, 2023, 2:01pm UTC](https://qa.fmod.com/t/connecting-dsps-vs-connecting-channelgroups/20477/3 "2023-07-31T14:01:15Z")
That doesn’t quite get to the root of my confusion.
The interpretation of the DSP graph seems pretty straightforward - each `DSP` sums its inputs, does its processing, and then sends its output to all the DSP’s that it’s connected to.
(here I’ll use `ChannelGroup` but generally this also includes `Channels` at the leaves of the tree)
The tree of `ChannelGroup`s is less clear to me. A lot of the documentation seems to assume a sort of “typical” arrangement where:
1. each `ChannelGroup` has a linearly-connected DSP Chain, where audio comes into the tail, passes through the chain, and comes out the head
2. each `ChannelGroup` has exactly one parent
3. If `ChannelGroup` A is the parent of B, then the output of B’s DSP chain head is connected to the input of A’s DSP chain tail
As far as I can tell, #2 is always true, but #1 and #3 are not, because you can manipulate the DSP connections separately, so for instance you could re-connect the DSP chain inside a `ChannelGroup` so that they are connected out of order, or have a branching structure. Additionally, you could disconnect a `ChannelGroup` head from the parent’s tail, and/or connect it to some other `ChannelGroup`.
As a concrete example, say we have `ChannelGroup`s A, B, and C.
- The parent of A and B is the master `ChannelGroup`
- A is the parent of C
- the output of C’s head `DSP` is connected to the input of the tail `DSP`s of both A and B
Questions:
1. does the fact that A is the parent of C have any impact here? Is that relationship different from the relationship between C and B?
2. It seems like most of the behavior is determined by the DSP connections, what do `ChannelGroup`s actually do?
3. Does the `ChannelGroup` structure put any constraints on the DSP graph structure?
4. What order do the DSPs execute in?
Part of the confusion is that a lot of the `ChannelGroup` actions have an impact on the DSP graph (e.g. `ChannelControl::addDSP` will connect the new DSP to the adjacent members of the DSP chain), but it’s not clear to me whether those are just for convenience, or are somehow fundamental.
---
### Author:  [@Leah\_FMOD](https://qa.fmod.com/u/Leah_FMOD)
#### Post date: [August 4, 2023, 2:10am UTC](https://qa.fmod.com/t/connecting-dsps-vs-connecting-channelgroups/20477/4 "2023-08-04T02:10:49Z")
> [@heavisideresearch](#):
>
> As a concrete example, say we have `ChannelGroup`s A, B, and C.
>
> - The parent of A and B is the master `ChannelGroup`
> - A is the parent of C
> - the output of C’s head `DSP` is connected to the input of the tail `DSP`s of both A and B
>
> Questions:
>
> 1. does the fact that A is the parent of C have any impact here? Is that relationship different from the relationship between C and B?
> 2. It seems like most of the behavior is determined by the DSP connections, what do `ChannelGroup`s actually do?
> 3. Does the `ChannelGroup` structure put any constraints on the DSP graph structure?
> 4. What order do the DSPs execute in?
While everything is built on and runs on DSPs, `ChannelGroup` was initially conceived of as a higher level macro control for child `Channels` or `ChannelGroups`, and it has evolved from there into a broader grouping as well. Interacting with a `ChannelGroup` interacts with its child `Channels` or `ChannelGroups` - while functionally it does interact with the underlying DSP chain, it is fundamentally different from just interacting with the DSP chain, which won’t actually add new DSPs or connections to the `Channel` or `ChannelGroup`.
The answers to your questions are as follows:
1. Yes. `ChannelGroup` API functions execute on child `Channels` and `ChannelGroups`. For the purposes of interacting via the `ChannelGroup`/`ChannelControl` interface, C is considered a child of A, but not a child of B; thus using the `ChannelGroup`/`ChannelControl` interface on B to interact with C will not work.
2. See my initial explanation in this reply.
3. It doesn’t _necessarily_ impose a constraint on the structure specifically, but the DSP graph will always be structured a certain way when interacting with it via the `ChannelControl` interface, and as previously mentioned the interface will not interact with arbitrary DSP connections.
4. To quote our [White Paper on DSP Architecture](https://www.fmod.com/docs/2.02/api/white-papers-dsp-architecture.html#order-of-execution-and-pull-no-pull-traversal): “The order of execution for a DSP graph is from right to left, but also top to bottom. Units at the top will get executed before units at the bottom.”
---
### Author:  [@heavisideresearch](https://qa.fmod.com/u/heavisideresearch)
#### Post date: [August 4, 2023, 5:33am UTC](https://qa.fmod.com/t/connecting-dsps-vs-connecting-channelgroups/20477/5 "2023-08-04T05:33:24Z")
Thanks, that’s super helpful.
> 1. To quote our [White Paper on DSP Architecture](https://www.fmod.com/docs/2.02/api/white-papers-dsp-architecture.html#order-of-execution-and-pull-no-pull-traversal): “The order of execution for a DSP graph is from right to left, but also top to bottom. Units at the top will get executed before units at the bottom.”
I’m assuming that has to do with the arrangement that you see when you open the FMOD Profiler tool, but it’s not clear how that’s affected by the code. Does it have to do with the order the `DSP`s were created, or the order they were hooked up, or the graph connections themselves (presumably you want each node’s to execute only after all its inputs).
---
### Author:  [@Leah\_FMOD](https://qa.fmod.com/u/Leah_FMOD)
#### Post date: [August 7, 2023, 2:03am UTC](https://qa.fmod.com/t/connecting-dsps-vs-connecting-channelgroups/20477/6 "2023-08-07T02:03:01Z")
> [@heavisideresearch](#):
>
> I’m assuming that has to do with the arrangement that you see when you open the FMOD Profiler tool, but it’s not clear how that’s affected by the code. Does it have to do with the order the `DSP`s were created, or the order they were hooked up, or the graph connections themselves (presumably you want each node’s to execute only after all its inputs).
Generally speaking, the arrangement of the DSP graph is determined based on the order in which DSPs are connected. However, the arrangement of DSPs is also affected by higher level groupings of DSP like ChannelGroup - logically, if you were to add a freshly created DSP effect to the first Channel created in the DSP graph, then that DSP effect will execute as a part of that Channel. That said, besides some niche cases, such as the reverb example listed in the DSP Architecture White Paper, the order of execution isn’t worth trying to control.
---
### Author:  [@heavisideresearch](https://qa.fmod.com/u/heavisideresearch)
#### Post date: [August 8, 2023, 5:40am UTC](https://qa.fmod.com/t/connecting-dsps-vs-connecting-channelgroups/20477/7 "2023-08-08T05:40:17Z")
Great, thanks. That’s very helpful.