Flat top Waveform when Recording from Cassette

I have noticed that, when recording from cassette, I get this strange waveform which has a much flatter “top” surface than bottom. This particular recording was made with the level set to record peaks at around -0.5dB.

To MY ears, it sounds fine on playback but something strange is clearly going on! I’m puzzled, any suggestions about what’s going on?

How does it sound?

It looks like an analog problem…

How is the cassette player connected to the computer? Are you plugged-into a microphone input on your laptop or soundcard? The mic input is “not correct” and many mic inputs are poor quality.

Headphone-out or line-out to line-in (blue on a regular soundcard) is OK. How to connect your equipment.

You might just try recording around -6dB or even a little lower. (1) I doubt that will fix the asymmetry but it’s worth a try.

Have you tried a different tape? I also doubt it’s the tape but you never know what the problem is until it’s fixed…

The positive (top) half of the waveform is “reduced” but the negative half is clipped.

The analog-to-digital converter is hard-limited to 0dB and usually there’s no problem getting close to 0dB. Again, I suspect your soundcard but it might be something else on the analog side.

If it sounds OK a high-pass filter should make it “look better” (without changing the sound) and give you more headroom for (digital) amplification. If this is music and there is deep bass that you want to preserve, a 20Hz high-pass filter will preserve the full audio range but it should kill the “offset” which is subsonic information.

(1) Digital levels are not critical as long as you don’t “try” to exceed 0dB. If you remember recording with analog tape, you wanted a “hot” signal to overcome the tape hiss. But with digital there is no tape noise. You can amplify digitally after recording. (When you’re digitizing a tape, the existing noise gets turned-down when you turn down the recording volume so it doesn’t hurt the signal-to-noise ratio.)

It’s the same for all tapes

The recording isn’t clipped, I think that the original must have been made with a limiter turned on as the peaks on all the tracks are remarkably similar.

My setup uses the PC’s line-in input, via a basic DJ’s mixer (2 phono, 1 line level & 1 mic). Waveforms generated when recording from vinyl don’t share this characteristic.

I wondered whether it was a characteristic of cassette recordings.

By the way, I CAN confirm that it has nothing to do with Dolby settings as waveforms from recordings known to have been made with Dolby and those known to have been made without all show this characteristic.


I think the most likely cause is something peculiar about my cassete deck, it wasn’t the most “state of the art”

I suspect so. It’s a very odd “characteristic”.

It’s either clipped or 'hard limited" on the negative half. When you push a limiter hard-enough it pretty-much becomes a clipper. :wink:

The tape itself is basically a limiter. It starts to soft-clip when it starts to saturate. (And the tape record/playback EQ further “softens” the distortion.)

Does it still look clipped on the bottom when you lower the recording volume?

I’m pretty sure it’s not tape saturation because the tape equalization tends to prevent (or distort) perfectly squared-off waves. …But it’s been a long-long time since I played around with analog tape.

Food for thought…

…Its’s all a bit academic because I’m not about to spend a fortune on new equipment and the main objective is just to get stuff onto CD in the best state that I can, within the resources that I have. BUT I’m intrigued now and (based on your observations) have a couple of experiments I’d like to try, I’ve even got some left over, good quality, pristine tapes I can use!

I’ll report back BUT, it may be a while. Thanks again for your input

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