Strange display of Audio Tracks

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RickyDee
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Joined: Sat May 08, 2021 12:16 am
Operating System: Windows 10

Strange display of Audio Tracks

Post by RickyDee » Sat May 08, 2021 8:53 pm

I'm new to Audacity and already appreciate it a lot. Here's my problem.

When capturing from my USB Turntable, the audio tracks look like they're supposed to look. But when I capture audio from my cassette deck through an EasyDay DC60 Video Capture Adapter, the audio tracks display incorrectly. You know how a waveform normally weaves back and forth between positive values and negative values (up and down from the 0.0 center line). Instead of the waveform going up and down from the 0.0 line, the waveform goes up and down from the 0.5 line. See attached screen shot. It sounds fine, I'm getting both channels, and each track shows the full scale of 1.0 to -1.0. But the audio waveform is only in the top half.

I have looked everywhere to find a setting that could change this but without any success. I look forward to an explanation with help on getting this to display correctly.
Attachments
Audio Tracks from Audacity.JPG
Audio Tracks from Audacity.JPG (70.06 KiB) Viewed 56 times

steve
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Re: Strange display of Audio Tracks

Post by steve » Sat May 08, 2021 10:23 pm

RickyDee wrote:
Sat May 08, 2021 8:53 pm
But when I capture audio from my cassette deck through an EasyDay DC60 Video Capture Adapter, the audio tracks display incorrectly. You know how a waveform normally weaves back and forth between positive values and negative values (up and down from the 0.0 center line). Instead of the waveform going up and down from the 0.0 line, the waveform goes up and down from the 0.5 line.
That's called "DC Offset" (the waveform is offset from the centre line due to a DC voltage).

It's quite common for consumer grade audio devices to have a tiny bit of DC offset, but the amount shown in your screenshot is extreme.
It is usually caused by a hardware fault, but very rarely I've seen it caused by a bug in the device driver software.

My guess is that the fault is in the EasyDay DC60 rather than the cassette deck, but you could test that by connecting a different audio source to the DC60 instead of the cassette deck (perhaps you have a CD deck that you could try). If the problem occurs with other devices, then the problem is almost certainly a fault in the DC60.

You can partially work around the problem by applying the Normalize effect with "DC offset correction" enabled, but really you need to fix or replace the faulty equipment.
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DVDdoug
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Re: Strange display of Audio Tracks

Post by DVDdoug » Sun May 09, 2021 12:19 am

It sounds fine
DC is zero Hz so you can't hear it (and it's probably filtered-out in your soundcard or amplifier, etc.). However, you'll hear a "click" or a "pop" at the beginning & end or when you start/stop playback or anytime the signal suddenly "jumps up" from zero.

If you filter-out the offset it should be OK.
and each track shows the full scale of 1.0 to -1.0.
These are the limits and if you "try" you go over +/- 1.0 (=100% =0dB) you get clipping (distorted waves with flattened tops & bottoms). The offset leaves less room for the waveform so you can't record at "full volume". That's a potential problem but your current waveform is fine and the Normalize effect will bring-up the volume.

:D :D The "DC60" has a DC offset! :D :D :D

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