FM3 USB I/O Buffer Size best practices?

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bikescene

Member
What does everyone set their USB I/O buffer size to when doing USB recording? I’ve been doing some searching on the forum, and I’ve mainly come across posts regarding the software buffer (eg. 128 samples vs 256 samples for glitch-free recording in the early days of the FM3). Can anyone comment on any balancing act that needs to be considered with the FM3’s hardware buffer?

I’ve only reamped with the FM3 so far, so I’ve adjusted the manual sample offset to account for any shifts in audio. On my system, a hardware buffer of 96 samples needs an offset of 400 samples, while a value of 1536 requires 1168 samples.

On the DAW side, I haven’t had any trouble during playback with 128 sample ASIO buffer, which gets reported as 8.67ms.

I haven’t tried recording and stacking tracks to understand the ramifications yet. I will give it a shot this week, but I wanted to see if there is a good starting point with adjusting this parameter for USB tracking.

Does the hardware buffer reset every time power is cycled? The value on my FM3 is set to 1536 each time I turn it back on, even though I’ve adjusted the value.
 
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As you probably know, there are problems with the buffer size and latency reporting. And, as you’ve discovered, there are problems when you attempt to adjust the buffer size. Assuming you’re monitoring direct, and assuming you’ve followed the instructions to adjust the manual compensation preference in your DAW, there’s nothing further you need to do. IOW, there’s nothing to be gained by turning down the buffer size when recording a direct monitored guitar.

You’ll find details here;
https://forum.fractalaudio.com/threads/latency-compensation-measurement.177851/
https://forum.fractalaudio.com/thre...rding-due-to-usb-latency-compensation.181686/
https://forum.fractalaudio.com/threads/axe-fx-for-the-recording-musician.177592/
 
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GlennO said:
As you probably know, there are problems with the buffer size and latency reporting. And, as you’ve discovered, there are problems when you attempt to adjust the buffer size. Assuming you’re monitoring direct, and assuming you’ve followed the instructions to adjust the manual compensation preference in your DAW, there’s nothing further you need to do. IOW, there’s nothing to be gained by turning down the buffer size.
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Thanks. I did read through 2 of the linked threads earlier in the week. Good to know that the hardware setting doesn’t need to be adjusted. I didn’t see the setting covered in the manual, but saw some forum posts briefly touch on it.

I was recording a performance on a MIDI controller with another interface yesterday and forgot to adjust the manual offset in my DAW back to 0. My notes were off just enough to annoy me.
 
Good point, I forgot to mention that. My comment about nothing to be gained by a low buffer size only applies when recording a guitar that is direct monitored. If you're playing a virtual instrument and using the FM3/Axe-FX as an audio interface, you definitely want the buffer size as small as possible. Until FAS fixes this bug, you're stuck with the convoluted procedure for turning down the buffer size. It couldn't hurt to contact FAS tech support to see about the status of a fix.
 
GlennO said:
Good point, I forgot to mention that. My comment about nothing to be gained by a low buffer size only applies when recording a guitar that is direct monitored. If you're playing a virtual instrument and using the FM3/Axe-FX as an audio interface, you definitely want the buffer size as small as possible. Until FAS fixes this bug, you're stuck with the convoluted procedure for turning down the buffer size. It couldn't hurt to contact FAS tech support to see about the status of a fix.
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Do you know if this bug is already fixed in in fw 6.0? Thx
 
jordikt said:
Do you know if this bug is already fixed in in fw 6.0? Thx
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It has been fixed for the AxeFX III and FM9. You’ll have to check with Fractal tech support about the status of the FM3.

Note that the fix is in USB firmware, not the DSP firmware, so the fix would not be in a DSP firmware update.
 
Yep, I would really like to see the USB latency issues fixed. Currently I am using SPDIF, but keep running into problems with my audio interface and the switching between internal and external clock. @rglr Improvements to the USB audio performance of the FM3 would be highly appreciated! :-)
 
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