CPU Economy Question

axme

axme

Inspired
I recently switched from AXE2 to FM3 so CPU load management is new to me. Several of my favorite presets are running around 80% CPU usage which could be the reason behind increased latency switching presets and scenes. I believe I’ve been frugal choosing reverbs delays and IR’s.

1. Do unused scenes in a preset contribute to CPU load?
2 Do bypassed blocks in a scene contribute to CPU load?
3. Is running stereo a huge hit to CPU?

Thanks
 
axme said:
I recently switched from AXE2 to FM3 so CPU load management is new to me. Several of my favorite presets are running around 80% CPU usage which could be the reason behind increased latency switching presets and scenes. I believe I’ve been frugal choosing reverbs delays and IR’s.

1. Do unused scenes in a preset contribute to CPU load?
2 Do bypassed blocks in a scene contribute to CPU load?
3. Is running stereo a huge hit to CPU?

Thanks
Click to expand...

1. No
2. Yes - whether a block is engaged or not has no effect on CPU usage. If the block is there, it uses CPU. But only if you are using THAT scene. Unless you meant preset.
3. Yes
 
Ron_R said:
1. No
2. Yes - whether a block is engaged or not has no effect on CPU usage. If the block is there, it uses CPU. But only if you are using THAT scene. Unless you meant preset.
3. Yes
Click to expand...
That makes sense. So basically when a preset loads, all the blocks are loaded. So it really doesn’t make sense to have multiple scenes to bring effects in and out and switching presets is more economical.
 
axme said:
That makes sense. So basically when a preset loads, all the blocks are loaded. So it really doesn’t make sense to have multiple scenes to bring effects in and out and switching presets is more economical.
Click to expand...
If you are trying to conserve CPU power, yes.
 
axme said:
3. Is running stereo a huge hit to CPU?
Click to expand...
Ron_R said:
3. Yes
Click to expand...
It depends.

Some blocks are stereo by default (reverb for example) so "running in stereo" isn't something you can chose to do or not do. In that case, it's not a huge hit on CPU. It just is. The CPU impact is a result of the reverb algorithm and quality settings you chose.

You have stereo capabilities in the cab block as well (panning an IR) that doesn't incur any additional CPU hit.

Using stereo delay algorithms consumes a little more CPU than the mono delay algorithms.
 
iaresee said:
It depends.

Some blocks are stereo by default (reverb for example) so "running in stereo" isn't something you can chose to do or not do. In that case, it's not a huge hit on CPU. It just is. The CPU impact is a result of the reverb algorithm and quality settings you chose.

You have stereo capabilities in the cab block as well (panning an IR) that doesn't incur any additional CPU hit.

Using stereo delay algorithms consumes a little more CPU than the mono delay algorithms.
Click to expand...
I stand corrected!

Yes, I assumed he meant like using two delay blocks, one panned left, the other panned right. That kind of thing.
 
These are best things I have found that you can do to lower CPU on the FM3 (as I too have an AFX2 which handles my needs with ease)...

a) If needing Reverb, use the Multi-Delay/Mono Diffuser instead with Master Time lowered.
b) Do not use the Cab Block's Preamp or Room Sound.
c) Use Standard Length IR's.
d) As noted above, minimize the number of Shunts used.
e) Run mono as much as possible.

My single preset handles the whole show as I need pristine cross-fades and tails, and the FM3 supports the following: 2 Inputs, 2 Outputs, Wah, Amp, Mixer, Cab (2 standard IR's), Pan/Trem, Pitch, Send, Return, 2 Delays, Multi-Delay, Vol/Pan, Plex-Delay, and 3 Shunts, along with stable response to automated Tempo/Fades/Cross Fades/Scenes/Channels from Ableton LIVE, along with 2 Stand-In Switches, an Envelope Follower, a LFO, the Arpeggiator, 2 Gates and 2 GEQ's (via the I/O's), and a few Control Switches. All of this at 77% - 78% CPU on average, with 81% - 82% peak on one Scene with the Pitch Block doing smart harmony, and the FM3 is stable on all 8 Scenes.

Note I'm on FW 5.01 as the latest FW 5.02 is too slow switching channels and bypassing the Pitch Block wile it's running Dual Diatonic via external MIDI commands at minimum.
 
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Ron_R said:
2. Yes - whether a block is engaged or not has no effect on CPU usage. If the block is there, it uses CPU. But only if you are using THAT scene. Unless you meant preset.
Click to expand...

I’m not sure this is correct. Once a Block is on the grid it uses CPU. This regardless of its state (bypass/on), the number of scenes or the selected scene.
 
From what I've been able to see, the real CPU hogs are almost exclusively the reverbs. Delays and amp models normally would be, but they share a dedicated core, so adding delays does not eat much CPU. This bugged me at first, but I just had to wean myself off of having that slight reverb at the end of each preset. All good after that.

I do find myself wishing the FM3 had a specific core for just reverbs, but I'm sure the FM3's architecture was planned around what DSP was available for the required price point, and the decision was made to put reverbs on the main core. More CPU would be nice, but the unit works and sounds so great as it is, I'm OK with swapping presets to manage CPU. No complaints.
 
axme said:
I recently switched from AXE2 to FM3 so CPU load management is new to me. Several of my favorite presets are running around 80% CPU usage which could be the reason behind increased latency switching presets and scenes. I believe I’ve been frugal choosing reverbs delays and IR’s.

1. Do unused scenes in a preset contribute to CPU load?
2 Do bypassed blocks in a scene contribute to CPU load?
3. Is running stereo a huge hit to CPU?

Thanks
Click to expand...

I've had to learn FM3 CPU 'economy' as well.

Generally speaking, for presets for live use, I am totally OK with ECONOMY level Reverbs. If I was recording, I may feel otherwise.

I think it's worth spending CPU to run 2 IR's, with 1 a few mm higher than the other, which adds depth to the tone.

Careful when changing channels in a preset that's already near the limit. For instance if you go from a Spring Reverb in Ch. A to some complex Reverb in Ch. B, the CPU usage will jump up when Ch. B is activated.

For ambient tones, often you can just use 1 PlexVerb block instead of a Reverb block, which saves CPU.

You can pack a lot into an FM3 preset - @Moke has a lot of great presets with an impressive amount of effects, for example.

Edit. Ultra Res is worth it to me
 
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As always, this community is a wealth of knowledge. Thanks for pointing out the Wiki Yek.
 
Solved. Thanks for all the tips. Reverbs were the main CPU hogs. IR’s at hi res we’re also a problem. My main patches are running in the low 70% CPU load now and don’t really sound any different.
 
axme said:
My main patches are running in the low 70% CPU load now and don’t really sound any different.
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And that's the key right there. Reduce CPU usage until you can hear the difference given the situation. It's amazing what sound that unit can put out as long as we don't overload it.
 
iaresee said:
You have stereo capabilities in the cab block as well (panning an IR) that doesn't incur any additional CPU hit.
Click to expand...
Correct me if I'm wrong, but you're just referring to panning a SINGLE cab, right? Because doesn't using two IRs eat up more DSP than a single one, regardless of panning?
 
I've just got an FM3 so this is a good thread - thanks @axme.

Does parallel routing affect CPU usage or would this only make an impact if shunts were involved?
 
Ugly Bunny said:
Correct me if I'm wrong, but you're just referring to panning a SINGLE cab, right? Because doesn't using two IRs eat up more DSP than a single one, regardless of panning?
Click to expand...
I don't recall seeing any CPU hit using either one or two IRs in a cab block. Maybe the cab block is in the dedicated core with amp mods and delays?
 
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