DC Bias/Phase Quirk

#1

Hello, been quiet lately because I’ve been working on learning the proper recording and mixing side of things, which has led me to a strange discovery. I’ve started recently using the SoundOut effect and piping channels into Ardour to flesh out tracks I was making before I started using SPi for MIDI sequencing. I’ve noticed some really weird anomalies from sounds that I record this way. Basses will unexpectedly warble and the bottom will disappear so that I have to boost and compress. I can see my <20hz rattling around. While I can use an HPF to fix that for a lot of sounds, it’s not practical on the bass. Also when I render out samples that are heavily chopped, (ie my breakcore tune) I can see what looks like a DC bias at the end of some of the slices, even if I chop off what I can see (yeah, I did that with every hat on a 7 minute breakcore tune :smiley: ) I still can hear ticking when the ample is in isolation. The final symptom of this issue comes up in Audacity. If I normalize with “adjust for DC bias” on it will actually offset the DC by the relative amount of level adjustment. One track I was working with last night is now entirely unipolar, which in this case is kind of cool because it’s some freaky bitcrusher mixing, but even if I add silence manually and play it back, the output reads 100%.

The only thing I can think of is maybe Mono is virtual in SPi and stereo subs are phase cancelling? Is there something I can do to ensure a pure Mono? SoundOut is still fairly new to me so I might be missing something.

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#2

Interesting. Do you see these issues with the standard stereo out signal?

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#3

Yes, just double checked. I started a pattern using the subpulse sent to stereo out routed to ardour, rendered, and checked in audacity. I tried both opening a single channel and the stereo pair and both gave a dc bias after a removal attempt. I did note that when i cut off the second half of the sample, including sound, that it reduced the amount of jump on the opening silence. I’ve ruled out the possibility of ardour causing it, i checked another recording that i rendered the same way but put a high pass on at 20 and it didn’t jump.
There doesn’t appear to be any phasing between the stereo channels, i did a phase inversion and conversion to mono both before and after normalizing (the inversion was first in all cases) and both came up 0. I’ll need to play with the recording in my eq to see if the warble itself is present still. Tomorrow morning if not tonight.

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#4

Apologies for the delayed response,

I meant do you see these issues if you don’t use any FX and just record the standard output of Sonic Pi :slight_smile:

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