Weird artifacts at high frequencies with logarithmic sine sweep

​I am using the Power Station (PS-2A) to capture high-quality impulse responses and am encountering two distinct acoustic anomalies that compromise the fidelity and flatness of the captured data.

Test Setup

Logarithmic sine sweep, from 20hz to 20000hz, normalized to -2dbfs. DAW track to SSL 12 line out to PS2A line in.

PS2-A to 4x12 16ohms cab. Depth and presence fully counter clockwise.

No clipping observed on SSL12 line out.

PS2 volume around 10 o’clock. Pretty loud but still clean.

​I am observing issues at both the low and high extremes of the frequency sweep:

​A. Low-Frequency Anomaly (20 Hz)

​When the sweep begins at 20hz I should only hear a faint sub-bass rumble (or nothing at all since guitar speakers don’t reproduce frequencies that low). Instead, I hear distinct sound content in the lower mids range.

​B. High-Frequency Anomaly (10 kHz and above)

​As the sweep moves into the high-frequency range (approximately 10 kHz and above), a distinct, unintended sound artifact appears. This is heard as a whistling or secondary sweeping tone that seems to go up and down in pitch, running in parallel with the main sine sweep until it stops.

Trying to pinpoint where those artifacts are coming from. Currently those artifacts are captured my the mics and skew my impulse response results.

​I can provide the sine sweep file used for testing, as well as a phone-captured video of the speaker output showing these artifacts, if they would assist your diagnosis.

​Thank you for your time and assistance.!

Welcome to the forum!

While we enthusiastically endorse tube amplifiers for guitar ampliification, that endorsement does not extend to impulse capture. For that we use and recomend a very linear solid state amplifier.

That’s not to say it can’t be done with a tube amp, and coincidentally, a couple of our gear users do exactly that, and seem very satisfied with the results. But again, it’s not something we would swear by.

Cheers,

Dave

Ok so you mean those artifacts are definitely produced by the PS2A and it’s tube amp nature?

I’m perfectly fine with it. For guitar amp attenuation/reamp it’s an amazing piece of gear.

For IR capture I’ll try to find a good flat low noise solid state power amp.

I’m not sure what artifacts we’re talking about specifically, but you are right, generally speaking. Definitely use a very linear power amp for making accurate impulses. Use the PS-2A power amp if you feel like exploring a rabbit hole or two.

Dave