My music files have been stuttering during playback.

I've been migrating data to new HDDs and doing lots of cloning (full 4Tb drives). I thought I was having end of life problems with the DAC is use between my iMac and my amplifier. The mp3 files kept cutting out, frequently for just a nanosecond, but enough to make the music unlistenable.

I went through every element, including moving the DAC to my living room and a different amplifier. Everything worked fine on the other amp. Music to the computer amp played via the headphone jack plays fine, so the amp's okay.

Playing music via the internal speaker works fine at any time, as do bluetooth ear buds.

Okay, the short story: the music plays fine, as long as I am not doing any copying of files. All the drives are connected by USB, as is the DAC. So, some sort of interference, I guess. I have some magnetic clips that will encircle cables and wonder if sticking one on each USB cable might help?

Any ideas what's going on here? Solutions?

Thanks.

 Unless your USB cable is very low grade or very long RF filters are unlikely to help. Launch About this Mac > System Report and under Hardware click on USB. It should look something like this. Find your DAC and see if there are any other devices connected to the same USB Hub. If so then try connecting your DAC to a port on another USB hub or disconnecting the other device(s) on the USB Hub the DAC is conencted to. (USB is a primitive, and somewhat noisy, protocol and devices like disk drives can compensate for errors, but your DAC can't.)

Thanks. You were right about the ferrite core cable clips not making a difference.

I've moved the DAC USB cable to a different input, the power cable to a different outlet than the drive caddies. I've even moved the iTunes folder to a USB-C input on the iMac.

Later (it's too early here right now, she is sleeping) I'll try to replicate the conditions and see what happens.

No joy, I'm afraid. I'll just have to listen to music by other means when I'm copying files from caddy to caddy.

Did you look at the System Report? There can be multiple ports on the same USB Bus and I would not be surprised if your MacBook Air only has a single USB Bus. That means data collisions are inevitable, resulting in the interruptions you are seeing hearing. There are technical solutions, but they would require adding a micoprocessor, and some buffer memory to the DAC.

Thanks! I'm actually working on an iMac with two USB busses, so your comment about the same bus gave me an idea:

I put all the docks (I've been calling them caddies) on the USB-C bus, and the DAC on the USB 3 bus. It worked. No more drop outs.

I had no idea what you were referring to as a caddie once again proving we are two peoples separated by a common language! Thanks for proving my theory

"If it ain't broke, don't fix it" is an axiom I have never quite embraced. You can always make things better, right?

So, I started moving things around and found myself back at ground zero. What I found: no matter which bus you connect the USB 2 DAC to, it will always show up in System Report as being on the USB 3 bus. The DAC has to be on the USB 3 bus (1 of 4 inputs), which means that the two docks have to be on the USB-C bus (only 2 inputs).

This is what I finally ended up with:
Connection scheme