disk too slow or system overload

The first thing you should do is make sure you have a current, full backup of your hard drive.

One test to perform is to log into another user account on your Mac and see if the problem persists there. If so then it's system wide and not just limited to your user account.

You have a couple of kernel extensions that are being blocked which seem to be related to audio:

Kernel Extensions:

/Library/Extensions

[Blocked] quantum_driver.kext (PreSonus Software Limited, 1.21.0 - SDK 10.11)

[Blocked] PaeFireStudio.kext (PreSonus Software Limited, 4.2.1 - SDK 10.8)

You should get a warning like this when it tries to load:

This Apple Technical Note, Technical Note TN2459, User-Approved Kernel Extension Loading, explains it and how to get them approved. I don't know if that's why the audio isn't playing properly but it's the only suspect in the report that caught my eye.

Check to see if there's is updated Presonis software available and install it.

Also you can download and apply the macOS High Sierra 10.13.6 Combo Update to reinstall the system and replace any possible damaged files.

You should backup your data. Drive is getting old. could use ccc to backup to an external drive. See if running from external drive solves problem.

I don't know why it would be too slow. You seem to have lots of processor power and memory left. That leaves reading the disk is too slow. Is this the original drive? Getting past its prime.

Use /Applications/Utility/Disk Utility.

Look for smart status of drive, if available.

run disk first aid.

Can you play other audio files outside of garage band?

Could try a safe boot.

Try a safe boot.

Shutdown your machine. Hold down the shift key. Poweron. The boot up will take longer than normal because the filesystem on the startup drive is being checked and repaired as needed. All about safe mode including what features and apps safe boot leaves out.

http://support.apple.com/kb/ht1455

I suggest you get an external harddrive and backup your startup disk.

Apple's Time Machine

https://support.apple.com/en-us/HT201250

Carbon Copy Cloner will copy your startup drive to an external firewire drive. You can boot from the external drive to verify that you have a good clone. When you upgrade your existing startup drive, you can at any time boot from your external drive and go back to your existing system.

http://www.bombich.com/software/ccc.html

SuperDuper is the wildly acclaimed program that makes recovery painless, because it makes creating a fully bootable backup painless. Its incredibly clear, friendly interface is understandable, easy to use, and SuperDuper's built-in scheduler makes it trivial to back up automatically. And it runs beautifully on both Intel and Power PC Macs!

Give SuperDuper a workout on your own system. Clone to your heart's content — for free. See what else is possible. When you're convinced that SuperDuper is a terrific solution — and a great value at $27.95 — you can register right from the application and start using its advanced features immediately!

http://www.shirt-pocket.com/SuperDuper/SuperDuperDescription.html

Download etrecheck. Click on the download link at the bottom of the screen. http://etrecheck.com/

Run etrecheck. The first five runs are free.

How to post etrecheck findings:

1) click on "Share report"

2) click on "Copy report"

3) Paste the information into an ASC forum reply.

Using EtreCheck by etresoft, the author https://discussions.apple.com/docs/DOC-11591

Stamp of approval https://discussions.apple.com/docs/DOC-8181

You are going to have to say more about your machine,

model, year, RAM, Storage. How much free space on your drive.

HDD or SSD

is this a recent problem, just started?

The no major errors are things that etrecheck knows about. We humans can still be better than a machine. Please post the results of etrecheck.

R