Strange result with line in recording: 5KHz cut off

The resulting audio is very tinny. 44.1Ksamples 32-bit, 48Ksamples 32-bit, 22Ksamples, 16-bit, ect… the same result:

Good frequency response up to 5KHz, then strong rolloff/cuttoff around 6khz, then a strange peaks around 14.5KHz and associated harmonics. The input audio should have components up to 20KHz (basically HiFi). I’ve attached a 2048 FFT with a hanning window on a 44.1K capture.

In general all audio sounds like 16kbps AMR or epub compression. Lots of aliasing and missing the entire upper band. I’ve used MME and Windows Direct Sound.

I have the same result on two laptop’s Line in port: MSI Wind U100 and an Asus K55N. Both have some kind of ‘intelligent’ Realtek sound card. I don’t appear to have too much control over it’s parameters (beyond selecting ‘line in’ or ‘microphone’ upon plugging in the 3.5mm audio cable).

Any idea what can be causing this? Are the line in ports on laptop’s limited to 5KHz in general? Maybe there’s a mains hum filter causing trouble?

If it’s a hardware limitation, any suggestion for a low cost USB sound card with decent performance (something with accurate reproduction up to 15KHz)? Or perhaps a low cost portable sound recorder device and bypass ‘on computer’ audio capture all together.
fft plot.jpg

What are you trying to record?

That’s unusual, and it’s especially unusual to have the same issue on two computers. (It’s also somewhat rare for laptops to have a line-input, but it’s not completely unheard of.)

Check Windows Control Panel to make sure there are no “[u]enhancements[/u]” being applied by Windows.

Normally, most soundcards will get close to the Nyquist limit (half the sample rate). Mic inputs on laptops & consumer soundcards are notorious for poor quality, but it’s usually a noise issue rather than a frequency response issue.

The line-input on a soundcard is often quite acceptable. Again if there’s a weakness, it’s usually noise.

You’re sure your source is “high fidelity”?

If it’s a hardware limitation, any suggestion for a low cost USB sound card with decent performance

Since it’s happening on two computers, I’m thinking it’s NOT a hardware issue. But, you did say both computers have the same Realtek soundchip & driver…

The [u]Behringer UCA202[/u] is reasonably priced, has good sound quality, and is popular (I don’t own one).

Note the most regular “USB soundcards” have only mic-in and headphone-out.

You missed some serious information. What did you plug into the computers?

It shouldn’t sound tinny. It should sound muffled. AM radio works out to about 5KHz and you’re not much higher than that.

I haven’t done an actual sound test yet, but I have a Zoom H4 and the idea of shooting a simple sound test just to see how it goes. There are other posters with stand-alone recorders as well. Tascam came up several times. NPR in the US used to use Tascam recorders for all their field productions. They may still.

Yes, about the fourth day of struggling with Windows sound management does make stand-alone recorders seem awfully attractive.