[serr]

Originally Posted by enuenu

Thanks for the input.
This is not a parameter I have ever touched. I always left it at default, mainly because I had no idea what it meant, I have a little more of a clue now. The greater the block size, the greater the latency but the better the sound quality, I think.

Nope. This is simply the control for the I/O buffer you tell your DAW system to use. Literally the time you give the computer to process audio before it has to hit the output. Audio quality in a DAW is only either 100% or 0%. It doesn't scale quality like a video responding to reduced bandwidth might. (Which would be a nightmare!) It would start getting dropouts. Very black and white.

So you have a choice in how to use your system.
Set it for a latency of under 11ms for live work. You will have less headroom for extra heavyweight plugins in this scenario.
Set it to "don't care" (eg 1024 samples) for post mixing work to give you more headroom for processing plugins since you don't listen to live inputs mixed with live outputs in this scenario.

Originally Posted by enuenu

Yes.

I hadn't used Reaper in a long while. So there have been quite a few OS updates since I last used Reaper on my iMac. I got distracted from DAW work and what I did do I recorded with GarageBand on iPad for idea collection. Been mostly playing through amps. However I am back into the DAW world.

When I fired Reaper back up in the last few days I made the awful discovery that I have this latency problem. Note that the problem is identical on GB on my iMac. GB never had this problem in the past on my iMac either.

Since you mentioned never actually setting your latency value with intention I'd say all bets are off for that following it.

Originally Posted by enuenu

Grill away, I appreciate it I have included links to screen shots of some preferences as they stand. The check box next to block size was not ticked. However ticking it made no appreciable difference to latency, still terrible, around 400ms. Either did changing it from values between 32 and 1028.
Screen shot 1
Screen shot 2
Screen shot 3

I see you're running some aggregate device configuration there. Sometimes using multiple interfaces together in an aggregate results in increased latency at the same settings. You may need to switch to only using the Apogee for the live sound work.

Question: I see you are not controlling the system sample rate from the device page. Are you controlling that with Reaper via the Project Settings checkbox or are you using a different audio app or control panel app to control your system sample rate?

SOP is to control both of these from the DAW app as first choice. Only go elsewhere if a device or use situation demands it.

If you were running at a different sample rate than your audio, Reaper would be converting everything on the fly and this sure wouldn't be a good scenario for live use either!

Originally Posted by enuenu

I used the driver search tool on the Apogee Website and they sent me an automated email based on my input. This email sent me a link to the relevant driver. However the link pointed to a message that said essentially said, "It's all good, you don't need a driver, the OS will recognise the device". Which it does.

That sounds correct and what I remember. Apogee uses the stock OSX driver.

Originally Posted by enuenu

Rolling back the OS sounds like a big job that could result in other unpredictable effects on my system. I'm guessing security issues would be a concern, as would compatibility with a whole lot of other Apple apps.

If you have a backup disk image of an old system it would be as simple as cloning it back to an active hard drive. If you don't treat your OS install like a resume and make backup clones like that... then it can spiral into hours installing everything manually from scratch. (Hint: Start making backups!)

Originally Posted by enuenu

Note that I still can't install the EFI. Part way through the attempt at installation the system tells me I need to be running 10.9.5 to install the file listed on the Apple support Website as the update to my machine's firmware???

I'll have to look this one up. I need to check out the new 10.12 update and see if they fixed their new trackpad feature too (the light tap = drag lock bit that's currently messed up).

I'm currently going back and forth between 10.6 and 10.10 systems at present for audio. I just blasted an additional 10.12 system on my laptop to check it out and act like I'm keeping up. I'd strongly recommend waiting on 10.12 right now from what I've seen too.
Rule of thumb in audio is to hang back an install or two on the OS unless there's a specific need.