Thankfully, any USB-C or USB-C-to-Lightning cable will do

You just connect one end of the USB-C cable to the Portacapture X8 (to its built-in USB port) and the other to your iPhone (USB-C or Lightning work, as suits your particular model of iPhone).

The Portacapture X8 can both record audio via USB and output it. It will automatically output it to any connected device that accepts it. As far as I can tell it uses the master track mix (there doesn’t seem to be any way to send multiple tracks simultaneously – I assume the USB audio protocol only allows a plain stereo transmission).

You must use 48kHz sampling

If you don’t, you’ll quickly get an error dialog on the Portacapture X8 saying “USB FS Mismatch”. That’s its daft way of trying to say that the receiving USB device won’t accept the sampling frequency it’s outputting. Why it can’t have a coherent error message, we’ll probably never know.

You can set the sampling rate in the “General Settings” app, under “Rec Settings” (along with the file format and bit depth / rate, though it doesn’t seem to matter what those are set to w.r.t. iPhone compatibility – they affect only recording to the microSD card).

You don’t have to use the iPhone to provide power

By default the Portacapture X8 will try to use the iPhone to provide power, rather than its batteries. But it doesn’t trust USB power sources – it will ask, via a dialog, “Is the AC adapter 1.5A or more?”. On USB-C iPhones you can power the Portacapture X8 over USB – by selecting “Yes” – although it will drain your iPhone’s battery. But whichever option you choose, the Portacapture X8 will then refuse to provide phantom power to your mics. If you’re not using phantom power then no worries, but if you are you must change the Portacapture’s settings – in “General Settings” app, under “Power/Display”, you must set “Power Source Select” to “Battery” instead of “Auto”. That will essentially turn off the Portacapture’s desire for power from USB, leaving USB as an audio channel only. With it powering itself from its batteries, the phantom outputs will work like normal.

You don’t have to record on the Portacapture X8

It passes audio through to the iPhone automatically, even if you’re not actively recording.

Thankfully the workaround is simple – disable tethering, or enable Airplane mode, while you’re using Image Capture.

• Permission errors with the destination folder (e.g. not writable by the current user).
• Conversion failures if you have the iPhone set to export images in “compatible” formats rather than their originals¹
• Unsupported image formats (e.g. HEIC) on very old versions of macOS (macOS 10.12 Sierra and earlier).
• The destination folder not existing.
• Etc.

Basically it seems like this “-9934” error is a catch-all for any kind of I/O error. Good job, Apple, in providing useful information to your users.

But add to the aforementioned list one other possibility, that I didn’t see mentioned anywhere: the destination volume is full.

I’ve been hitting this error message in Image Capture sporadically for months and been baffled by it – especially since it seemed to occur for seemingly random sets of images and videos, that were sometimes consistent between attempts and sometimes changed unpredictably. Which is of course the result of the destination volume being perpetually close to full but varying slightly over time as random bits & pieces are added or removed from it.

It’s especially tricky because the destination volume won’t typically show as actually full, in the Finder – it could have virtually any amount of space left, even hundreds of gigabytes, because the particular image or video that hits the limit could be huge, and Image Capture either tries to pre-allocate the entire file’s space up front (failing immediately if there’s insufficient space) or retroactively zeroes out the file if it encounters a write error. Either way, it leaves a bunch of zero-byte files (the failed transfers) behind, rather than incompletely-written ones, further hiding the fact that it ran out out of disk space.

1. Please don’t ever do that. It means transcoding your original images from DNG or HEIC into JPEGs, increasing their file size and/or reducing their quality in the process. Don’t do it. DNG and HEIC are old formats that are widely supported – not just on Apple devices, but Windows as well (and probably most Linux distros). ↩︎

e.g. I thought I’d give it a whirl as I was flying out of Houston, out over the Gulf of Mexico. Alas all I got was a blunt denial:

So don’t actually travel to remote places and expect this feature to work. 😔