flat bottom on waveform

I have seen some posts on flat waveforms, but my problem, (if it is a problem), is that only the bottoms of the waveforms are flat. The tops look normal.

I am using Windows 7 Home Premium, and also using a pre-amp from my turntable to the computer input.

Without the pre-amp I don’t have very much signal input and have to amplify every recording to get close to normal output.

Does anyone know why only the bottoms are flat? The rest of the waveform looks normal, including tops and middles.

Could you post a short sample? Just 3 or 4 seconds in WAV format will be fine.
See here for how to add attachments: https://forum.audacityteam.org/t/how-to-attach-files-to-forum-posts/24026/1

Would like a portion of the audio or a JPG from a screen shot?

I’ve been trying to attach a wav file, but my upload link (dishnet) is crawling. After 10 minutes, it’s stuck on 2%.

I’m substituting a JPG for looks. I may be able to FTP it, if you’d like.

Forgive my ineptness. I was trying to upload too large a file in wav.

Here is about 5 seconds worth.

Yes that is clipped at the bottom, so you do have a problem.

Please say more about the equipment - what sort of pre-amp, what input on the computer, what sort of turntable, what sort of computer… too much detail is better than not enough.

The pre-amp is ARTcessories DJ Pre II, computer input is standard stereo mini-plug, with RCA jacks into the pre-amp, computer is generic w/ Asus M3A-78T MB; Technics turntable.

Onboard Realtek is the audio I/O device. Using 4MB RAM, 2.60 gigahertz AMD Phenom 9950 Quad-Core. Speed is no problem.

I see this quite frequently in audio (uploaded as video) on YouTube. I have never seen it on any of my own recordings.

Does it have separate Mic input, Line input and Line/headphone output?

The Realtek onboard does, including front panel inputs, but only the line-in and line-out at the back are in use.

Correction to the last post.

Mic input on front, with headphone out.

It’s also out of balance. The top wave is larger than the bottom wave and is hiding the fact that both waves clip at the same point. The bottom wave only occasionally gets to the clip point, whereas the top wave lives there.

Mic input on front, with headphone out.

You can’t use Mic-In as a generic audio input. For one thing it’s rarely stereo and it’s really easy to get distortion such as this.

If you are using the Mic-In, you should stop doing that and create very good stereo Line-In connections with a Behringer UCA202 or equivalent.


I am using the line-in connection on the back of the board. BTW, I have tried uninstalling the re-installing everything, but that did not correct it.

If you have any other ideas, or anyone else knows of a fix besides the one you mentioned, I would appreciate hearing from them. And thanks to you for all your attention on this.

Do you have an iPod or other personal music player? Jack that into your sound card in place of your turntable system and see if you can make a good recording that way.


If not, then the Line-In electronics may be damaged. If you can, then there’s something wrong with your preamp – probably.


Audacity doesn’t apply effects or filters in real time and it’s a complete slave to what the computer is doing. If the computer supplies damaged sound, then that’s what gets recorded. Koz

Thanks for those tips. I’ll check those out tomorrow, when I have some more time. I’ll get back if I learn anything from those two points.

After doing some more checking, I discovered the fault was in my setting for gain trim on the pre-amp.

The instructions say to set the gain to the point where the LED glows red and then back off from that so there is no red. I believe the red LED indicates distortion.

That setting put the gain at +6 - +8. But when I dialed it back, things improved. I ended up moving it to just slightly over 0 DB, the flat bottom disappeared, and waves look normal now.

I still have to amplify in Audacity, usually upwards of 8.5 - 9.5 to come up with Audacity’s adjusted version of the audio signal.

Another thing I checked was my stylus, which was well used, but apparently still in good shape.

Thanks so much for your suggestions. You put me on the right track, and I think everything’s now okay.