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UAD Arrow + External D/A converter (no spdif out)

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UAD Arrow + External D/A converter (no spdif out)

Postby Kato » Thu Apr 22, 2021 8:25 pm

I'm thinking about buying an external D/A converter to upgrade the sound of my home studio (recently revamped the studio with a proper acoustic project and treatment).
I`m currently running an UAD Arrow - I don't need a lot of inputs here in the studio and I enjoy the onboard processing/plugins.

The typical solution I found on forums was to use the digital out of the interface going to the DA converter. But since the Arrow does not have a digital out I setup a test using a portable USB DAC: I created an aggregate device on my Mac (UAD Arrow + USB DAC headphone amp), and selected the device on Reaper.
I was able to monitor via the USB DAC, and the UAD inputs were available and I was able to monitor the analog inputs.

The idea is to record using the Arrow, and to use the external DAC as the monitor.
For my MAC system sound and general music listening I could just select the DAC directly without the aggregate device.

Everything seems to work fine. Are there any potential clock issues degrading the sound that I didn't notice at first? Am I missing something, or the solution for an external DAC is just as simple as an aggregate device?

I just want to make sure this is a proper setup before spending money on an USB D/A converter.

Thank you!
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Re: UAD Arrow + External D/A converter (no spdif out)

Postby CS70 » Fri Apr 23, 2021 8:07 am

Kato wrote:Everything seems to work fine. Are there any potential clock issues degrading the sound that I didn't notice at first? Am I missing something, or the solution for an external DAC is just as simple as an aggregate device?

If you don't have a word clock connection between the two devices you are aggregating, the software will have to guess a common clock, and as a consequence your recordings and playbacks won't likely be sample accurate.

In fairness, the software seems to do a pretty good job at that, as it seems that most people dont even realize the issue exists. But then most people listen to low bitrate mp3s :D If you want the best possible quality, you need a shared clock between the devices.
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Re: UAD Arrow + External D/A converter (no spdif out)

Postby Hugh Robjohns » Fri Apr 23, 2021 8:58 am

Surely it depends on the design of the USB DAC?

Most these days are asynchronous types and the DAC itself essentially pulls data from the computer when it wants it, determined by it's own internal clock system, rather than being pushed data from the computer whenever the computer gets around to it.

So a shared clock between input A-D and monitoring D-A is not actually necessary in this situation.
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Re: UAD Arrow + External D/A converter (no spdif out)

Postby CS70 » Fri Apr 23, 2021 10:50 am

I don't know - we'd have to know more on how the aggregation software corrects for drift? It may also depend on what exactly the OP is trying to do (i.e. just listening, or listening to playback and monitoring the inputs at the same time?). What I'm thinking is that the aggregation software still needs to place data in output buffers (so that the device can pull it) and will do so based on approximation of the actual timing for the non-master device.
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Re: UAD Arrow + External D/A converter (no spdif out)

Postby Hugh Robjohns » Fri Apr 23, 2021 11:00 am

CS70 wrote:What I'm thinking is that the aggregation software still needs to place data in output buffers (so that the device can pull it) and will do so based on approximation of the actual timing for the non-master device.

Sure, but as long as the output buffer is big enough there shouldn't be a problem.
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Re: UAD Arrow + External D/A converter (no spdif out)

Postby merlyn » Fri Apr 23, 2021 1:25 pm

CS70 wrote:If you don't have a word clock connection between the two devices you are aggregating, the software will have to guess a common clock, ...

You've posted this before and it is completely wrong. Core Audio uses re-sampling to synchronise two devices that don't have word clock.
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Re: UAD Arrow + External D/A converter (no spdif out)

Postby CS70 » Fri Apr 23, 2021 6:59 pm

merlyn wrote:
CS70 wrote:If you don't have a word clock connection between the two devices you are aggregating, the software will have to guess a common clock, ...

You've posted this before and it is completely wrong. Core Audio uses re-sampling to synchronise two devices that don't have word clock.

You sound like my ex. What is completely wrong? :lol:
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Re: UAD Arrow + External D/A converter (no spdif out)

Postby merlyn » Fri Apr 23, 2021 8:53 pm

CS70 wrote:What is completely wrong?

The only guessing involved in an aggregate device on a Mac exists between your chair and keyboard.

@Kato If you're after supreme quality I wouldn't have thought you want re-sampling as part of the signal chain.
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Re: UAD Arrow + External D/A converter (no spdif out)

Postby Kato » Fri Apr 23, 2021 9:55 pm

Hugh Robjohns wrote:Surely it depends on the design of the USB DAC?

Most these days are asynchronous types and the DAC itself essentially pulls data from the computer when it wants it, determined by it's own internal clock system, rather than being pushed data from the computer whenever the computer gets around to it.

So a shared clock between input A-D and monitoring D-A is not actually necessary in this situation.

Thanks!
I'm thinking about a RME ADI2.

I would be listening to music using the ADI 2 exclusively.

With the aggregate device setup I would be using:
While mixing since it would be nice to use the UAD plugins with the ADI2.
For recording, I could use the Arrow preamps and A/D and monitor through the RME.

But if the whole resampling issue discussed here defeats the purpose of having an external DAC, maybe it would only make sense with an interface with SPDIF out (closest thing would be a UAD x4).

In the end, I'm still wondering if the "better" DAC would be a good addition to the home studio setup...

Thanks you all for the support. This forum is the best.
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Re: UAD Arrow + External D/A converter (no spdif out)

Postby CS70 » Sat Apr 24, 2021 5:25 pm

merlyn wrote:
CS70 wrote:What is completely wrong?

The only guessing involved in an aggregate device on a Mac exists between your chair and keyboard.

Ok :D
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