AM4 USB Audio questions

D

DC/DC

Member
Hi everyone,

I posted this question in the Announcing the AM4 thread, but it may have gotten lost in the shuffle, so reposting here.

I’m a VP4 user who is considering purchasing the AM4. I’ve read multiple threads & watched some videos, but would like some clarity on the actual USB Audio capabilities.

The AM4 is described as both 4x4 and 2x2 on the product page & manual, and the wiki page says “4 channels (4x4)”. To me, these all mean different things and it’s a little confusing.

Typically, for other audio interfaces, the I/O implies simultaneous usage. For example, 8 x4 would be interpreted as 8 input channels and 4 output channels (total of 12 channels) that could be used simultaneously.

The AM4 webpage states “You can record the AM4’s processed outputs or capture a DI for re-amping. You can play back computer audio through the AM4’s stereo outputs, or send tracks to the unit for processing, including re-amping.”

The word “or” is mentioned multiple times, which could be interpreted as only 1 option at a time. “Or” does not have the same meaning as “and” which implies capability of simultaneous usage.

So if the AM4 has 4x audio/usb channels, would a more accurate description be “the AM4 could be used as a 4x0, 2x2 or 0x4 interface”?

I’ve studied the block diagram and understand the overall signal flow options. I’m seeing could be done for routing, but it’s not clear to me if there are any built-in constraints (I.e., USB channels 1 & 2 can be used for Rec or Play, but not both at the same time…must be one or the other, etc.)

TLDR - I’d like to do the following with my DAW & an AM4 connected via USB:

1) Record the AM4’s stereo output w/ amp modelling, fx, etc while simultaneously recording a separate dry DI track (doesn’t matter if the DI is mono or stereo).

2) Take that DI track and reamp it through the AM4 while simultaneously recording the AM4’s stereo output.

Apologies for the long-winded post. It is not intended to be a criticism by any means.

Could anyone who has actually used the AM4 USB Audio and/or Fractal please clarify what the actual capabilities/constraints are? Thanks!
 
@FractalAudio

Do the USB 1/2 outputs mix into the Insert Send, or into the Headphone and Main outs ?

The block diagram in the manual says they mix into the Insert Send -- is it right ?
 
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Can someone please check whether USB 1/2 audio output comes out of the Insert Send ?

The block diagram in the manual (page 68) says it does, but I don't necessarily believe it.
And I would prefer if USB 1/2 only came from the main out.
 
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@FractalAudio

Actually, page 68 of the manual contradicts itself.

The upper diagram shows USB 1/2 mixed into Insert Send.
The lower diagram shows USB 1/2 mixed into Out L/R.

(Also see page 15, where lower diagram presumably comes from.)

As @mr_fender pointed out, USB 1/2 is almost certainly mixed into Insert Send, because that's where the single D/A converter is.
 
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USB playback is mixed in digitally before the converters, so there is no distinction either way. The insert and output jacks are in series, so the post converter analog signal has to go through the insert to get to the output jacks.
 
AlbertA said:
? No? What do you mean?
Click to expand...

Suppose:
  • You put your favorite pedal in the loop.
  • You play backing tracks on USB 1/2 using your phone.
  • You monitor via Out L/R or the headphone out.

Then:
  • The backing tracks are processed by the pedal.

Which is probably not desirable.
For this scenario, it would be better to mix USB 1/2 into Out L/R and the headphone out.
But as mr_fender points out, there's only one D/A converter available.

Note: This scenario doesn't bother me that much. And we can't change the hardware. But someone can fix the diagram on pages 15 and 68 of the manual -- USB 1/2 feeds Insert Send, not Out L/R. And as this scenario shows, it makes a difference.
 
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davidespinosa said:
Suppose:
  • You put your favorite pedal in the loop.
  • You play backing tracks on USB 1/2 using your phone.
  • You monitor via Out 1/2 or the headphone out.

Then:
  • The backing tracks are processed by the pedal.

Which is probably not desirable.
For this scenario, it would be better to mix USB 1/2 into Out 1/2 and the headphone out.
But as mr_fender points out, there's only one D/A converter available.
Click to expand...
Yes, but @mr_fender was saying there's no distinction from the point of view that it has to be mixed before the DAC regardless of whether you use the loop/insert or not.

And yeah there's only one DAC with 2 differential output channels (L and R): https://thegearforum.com/threads/fractal-audio-systems-am4-amp-modeler.10317/page-69#post-439319
 
AlbertA said:
Yes, but @mr_fender was saying there's no distinction from the point of view that it has to be mixed before the DAC regardless of whether you use the loop/insert or not.
Click to expand...

* There's a distinction between Insert Send and Out L/R. That's clear.

* There's a distinction between a hardware design where USB 1/2 feeds Insert Send, and a hardware design where USB 1/2 feeds Out L/R. See the above example.

So where exactly is there "no distinction" ?

You guys are probably saying that if there's only one converter, then there's only one possible place to feed USB 1/2. I agree. But I don't see how the language "no distinction" expresses that idea. I can only read your words -- not your minds.

Again, my primary goal is for the manual to reflect the hardware.
 
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There is no distinction because there is only one path for the analog audio to take and that is through the insert to the output jacks. There is no way to separate them.

If the USB diagram showed that USB Outputs 1 and 2 went to the insert instead of the output jacks that would probably confuse people even more. The output jacks are the ultimate destination for monitoring, not the insert.
 
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I just tested this with a drive pedal in the insert and the backing track from my computer is in fact processed thru the drive pedal when enabled.

AM4 USB to computer, AM4 out to FRFR

EDIT: Not an issue for me as I am not using the insert, just had some free time and was curious.
 
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