I'm an amateur keyboardist who recently moved to another country and started a new music corner in my new flat.
In my previous place I still have a Presonus 1810c (which I love and trust) and some analogue synths.
My instruments here are my little Eurorack modular, a Korg MS-20 mini and a Presonus 1824c interface that I got for a bargain price on eBay (hint hint?)

It turns out that everything that goes into the 1824c seems to lose bass frequencies.
The instruments sound fine when I plug my headphones directly into them, but there's this problem when they go into my PC.
Unfortunately I don't have my 1810c with me to make a comparison.

I'm attaching some screenshots with an oscilloscope and a meter: several waveforms from an oscillator at 62 Hz, directly into an attenuator as close as possible to clipping my AD input (about 1/3 Eurorack level out - see photo names for details). Different oscillators give the same result.

For reference, there's also a square wave from a VST at 62 Hz, which has less high frequencies, but that's a real straight line on the meter - as it should be.

(I know my AD is not DC-coupled, so technically the oscilloscope is not that useful)
I tried all eight AD inputs with all three mini-jack-to-jack cables I have here.
One of the cables also "sounds" very low in volume (going in the bin tomorrow), and the loss of bass happens with all three cables. Are they all broken?

This happens at both 44.1 kHz and 48 kHz.
When the inputs are routed directly to the outputs (ie no DAW) it still sounds HPF'ed... but I can't measure it, and tbh after an hour of listening to a 62 Hz square wave it's hard to even guess.

EDIT: I'm always monitoring through the same headphones, I don't have any speakers (yet).

Is there anything I can try? Did I get a broken interface? Is this a known problem? Can it be fixed?

Thank you so much in advance!

Cheers

I am not quite understanding all the details of your setup. Are you saying that it sounds high-passed from your PC when those same headphones are plugged into the PC (or interface?) Or are you listening to the PC on speakers?


I'm attaching some screenshots with an oscilloscope and a meter: several waveforms from an oscillator at 62 Hz, directly into an attenuator as close as possible to clipping my AD input (about 1/3 Eurorack level out - see photo names for details). Different oscillators give the same result.

so your signals are measuring correctly internally?
That would be one hell of a coincidence. These are the same cables you used to use before? Cables don't normally "start" to high pass. Never mind 3 cables at once.

If you can't measure it, that still leaves monitoring as a suspect. You said you checked this by plugging your headphones into your synths. Are you also monitoring your
DAW with those same headphone? But if this is being listened to on speakers, all bets are off. Maybe the fact that you are in a corner has something to do with it? You are in a new room, after all.

You can borrow a different interface to try. Seems like a long shot, but you never know. You could move your setup to a different spot. You could rip a CD and compare some commercial recordings coming out of your interface to the same recordings coming out of a CD player or some such using the same speakers. .

Yes, I forgot to mention it: I'm always talking about the same headphones. I don't have any speakers unfortunately.

Yes, everything works fine internally, and all the outputs sound great and full when playing VST, audio, etc. The problem is on the signal coming from my synths to my computer.

Thank you!

ok that lets out room acoustics and expectations

I did not really follow your test methodology but I don't understand how they can 'measure correctly', then.

I see that the interface has combo jacks in the front for mic/instrument/line. Have you tried plugging the synths into the line inputs in the back? Or if that's what you are doing, maybe plugging them into the front? Some synths seem to work better going into "instrument" and others are fine with "line". There seem to be switches in the front for that.

Another long shot idea: most interfaces these days have a software cue mix app that allows you to monitor at low latency, adjust routings etc. Many of those apps have the ability to host plugins. On my interface (a UAD) you even have the choice to record with those plugins or just use them on monitor.

You could check that app. Perhaps the previous owner left some effect on there that doesn't go away when you shut down?

Some updates: I had a chat with the Presonus support and they think it might be a hardware issue.
As it's second-hand, it's out of warranty, so it sounds like a hard-learned lesson about checking items before the eBay 30-day warranty expires.

I have tried everything you suggested apart from using a XLR connector. Definitely worth a try before trying to re-sell it hoping to get at least some £ from it. Thank you!

Does the Presonus have its own little Mixer app?

The amount of times these things, from anyone (Rme, Audient, SSL, Prism etc), are feeding stuff back round itself etc.

Tracked a weird problem down last week to an almost unnoticeable fader up on a channel on a silly app.

I have a preset for the app on my Apollo interface called "NOTHING". All the inputs are down, all the auxes are muted, nothing is coming in. That way if there is drum mic left up, or a DI bass still pluged in, I won't hear any strange sounds when I am mixing or just listening.

For some reason it always claims the preset has been "modified" when I shut down. It hasn't. but I always say "no" to keeping any 'changes'

I don't know anything about these synth units so take this for what it is worth, you're not connecting a stereo output signal to the balanced mono inputs on the interface with a single cable are you? If you did that everything common on the L and R gets cancelled.