[SOLVED] Baseline of waveform at 0.5, recording tape via EasyCAP

I’m trying to record my old cassette tapes and have bought an EasyCAP phono → USB converter.

However, when recording in Audacity the baseline of the waveform centers at (+)0.5 (please see screen dump).

The audio quality of the recordings sound fine, but the input is pretty low. My tape recorder has an output volume potmeter which should normally be set at 50% output level when playing over my stereo. I can raise the volume, but then the recorded audio quality gets distorted (shown in the right part of the screen dump).

I have not experienced this before, but have never worked with (PC-)external sounds in Audacity before.

Any suggestions on what is going on or how to correct this


Seems like there is a rather big DC offset.
Try this:

Go to effects ----> Select High Pass Filter,
Then enter 10 Hz for frequency and roll-off of 12dB/octave.
Screen Shot 2022-01-07 at 3.11.50 PM.png
Another way is to use the Normalize feature of Audacity.
This will remove any DC and adjust the level of your audio to any desired level.
I used -12dB but depending on your application, you may want it higher.
I suggest you always leave a bit of headroom, so don’t go higher than -1dB.
Screen Shot 2022-01-07 at 3.16.32 PM.png

Understatement of the year … :nerd:


Could be worse.
Don’t know how, but it could.
Still have from 0.5 to 1.0 to fill up. :smiley:

Wondering where all that DC is coming from.
I’m guessing a combination of DC present on the output of the tape recorder/player
and insufficient filtering on the input of the USB device.

Either way, it’s not a good situation.

@ Uglspil

Where are you taking the output from the tape player?
Is it perhaps the headphone output?
Does it not have a Line-out that you could try with?

Another test you could try, connect nothing to the input of the USB device
and record a few seconds.
If the DC is still there, then it’s some kind of bias on it’s input.
Send it back for a full refund.
It’s either faulty or has a serious design flaw.

If there is no DC, then it is coming from the tape player.

Thank you for your kind answer - and sort of problem solving.
Result: EasyCAP is the culprit. I’ve used it with OK results for recording old VHS-tapes, though, so it isn’t going straight to the bin.

I am using the line output on my pretty good Denon cassette recorder, which for some odd reason has adjustable output.
On the screen dump below you can see a recording (of nothing) on the left hand side, and on the right hand side with the EasyCAP USB plugged into the computer but with no further connection.

I’m now gonna borrow a Behringer audio interface from a friend instead.

Thanks again.
Cheers /Steffen

Hi Steffen

Glad you got it sorted out.
Denon products are pretty good so not surprised that it’s not the problem.

As to the adjustable output, that is actually a very good thing.
Domestic audio devices like amplifiers, tend to be more “deaf” than professional counterparts, hence the level control to compensate for this.
This then, allows you to set the 0dB reference for any unit it’s feeding into.

As to your USB device, it’s now obvious that it has some kind of DC bias on its input and is dependent on the impedence of the device feeding it.

As a quick experiment, connect a pair of cheap headphones to the input of the USB device.
You will have to use a converter from 3.5mm stereo to RCA.
Then, record a few seconds of silence.
Has the DC level gone down?
If yes, then it conclusively proves a DC bias that is pulled down by the impedence of the input device.
In this case, the headphones which are probably somewhere between 8 and 60 ohms.

You will find that the output impedence of your VCR is lower than that of your Denon.
As a result, the DC level is lower too, but I’m willing to bet it’s still there.

Denon normally are pretty good - BUT the EasyCAP USB looks like a cheapo device.

@Steffen: you say you are going to borrow a Behringer interface (UCA-202?) - I would expect much better results with that.


waxcylinder wrote:

…the EasyCAP USB looks like a cheapo device.

Completely agree.
Most of these generic USB type grabbers are of very low quality and have dubious circuits.
They are designed and built to a price and if 0.001 cent can be saved by leaving out a capacitor,
they will do it without hesitation, with no regard for the consequences.

It is worth the extra expense of getting something made by Behringer, Mackie or my favourite, Focusrite.