ChrisNinety

Hi experts, and happy new year!

I have a Mackie Onxy 1620i that I run with Logic 9.1.6 on a Mac Pro and I've struggled for a while with some very subtle tuning issues. Certain tracks just seem to not be in tune with the others, but I chalked it up to temperamental guitars or my pitch perception.

The other day, I decided to track it down. I used the best tuner I have (a Sonic Research LED strobe tuner, considered extremely accurate), and I generated test tones in Logic a bunch of different ways. Long story short, I discovered that every time I change the sample rate (from 44.1 to 48, etc.), or turn the Mackie on and off, the pitch of the test tones read slightly differently on the tuner. Everywhere from +3 cents to -3 cents, for a range of 6 cents (definitely audible, unfortunately). There is no consistency to it, other than the fact that it's consistently different.

I unplugged the Mackie and measured the same tones directly from the built-in audio of the Mac, and they read dead on in tune.

I then went and rented another interface to do a comparison. I chose a USB 2.0 interface to see if that might make a difference (the Mackie is Firewire), so I picked a Focusrite Scarlett 18i6 and did the same test. In my testing, the Focusrite reads slightly out (about .7 cents), but at least it's consistently out across sample rates and restarts. So, if I adjust Logic so the test tone plays in tune, record it, bounce it, restart my rig, bring it back in, and test it again, it reads perfectly in tune. I can't do that with the Mackie.

I also redid the entire test on another Mac altogether and got exactly the same results. So, it seems to be down to the audio interface for sure.

So, a couple of questions:

- My guess is the Mackie isn't always running exactly at the requested sample rate, and it seems to change to a different (maybe random) incorrect sample rate when restarted or the sample rate is manually changed. Does this sound right?

- The Scarlett is much better because it's consistent, but it's still off by a little less than once cent, whereas built-in audio is 100% perfect. Before I go down a rabbit hole trying every interface under the sun, does anyone know what the correct expectation is? Is less than 1 cent as good as I'm going to see from a reasonably priced interface?

To put it in terms of sample rate, I did a little math. This is my best guess, but there could be flaws in my logic, so please feel free to correct me!

- Using 440Hz as my baseline, .7 cents flat is 439.8Hz.
- 439.8 is 0.999545454... of 440.
- Applying that same percentage of difference to the sample rate of 44100 gives me 44079.95.

So, it looks to me like the Scarlett is running consistently at about 44080 samples per second instead of 44100. Should I expect better than that?

The Mackie is worse. If the above logic is correct, it will go as low as 44019, or high as 44180, but being inconsistent makes it just impossible to live with because I can't even compensate for it.

I've done a bunch of searching on this topic both here and all around, and I literally could not find a single bit of info on audio interfaces negatively impacting pitch. Maybe I'm using the wrong terms, but I just couldn't find anything and would love opinions from the folks here.

Thanks for slogging through this whole post!