Flat Top Waveforms in Cubase. MOTU 828mkII & 8Pre.

Sometimes I get a waveform in which the top is flat. As if the upward peaks hit a brickwall limiter, but the downward peaks are normal. This occurred using Cubase SX2 with the MOTU 828mkII and MOTU 8Pre. I don’t know if this is a DAW issue or hardware issue.

At first this phenomenon only occurred with two identical CAD mini condenser mics we use for drum overheads into the 8Pre connected ADAT to the 828mkII, so I thought something was wrong with those cheap mics. But, later the exact same thing happened to a Bass guitar track recorded through an ART tube preamp and into a line input in the 828mkII.

All other tracks recorded normally (peaks appear normal up & down) and simultaneously using every available input of the 8Pre (8 Mics) & 828mkII (8 Line in, 2 SPDIF) except for the 2 mic preamps on the 828.

This happened sporadically after we added the 8Pre on a PC with WinXP SP3 and Cubase SX2 which I have used for years without issue. I have recently upgraded the same PC to Win7 64bit and Cubase Elements 7. I haven’t recorded with the new setup long enough to know if it is still affected. But the old projects draw the waveforms the same way in Cubase Elements 7, so I think the actual files were recorded that way.

I wanted to know if anyone else has experienced this as well.

I thought I had resolved this issue by turning the phantom power off then back on for the condenser mics and adjusting the settings of the tube preamp for the bass guitar. Afterwards, the tracks recorded with normal waveforms for the rest of the day.

However, when i returned for the next session and began recording the flat tops were back. The bassist swore he didn’t touch the preamp, and I switched the phantom off and back on again for the mics, but no luck. I even unplugged the cables from the interface and put them back in, but that didn’t help either.

I am wondering now if the culprit is just faulty/cheap cables. I am going to try some different cables next session. Also, I never checked another DAW to see if it was the software or hardware causing the issue. I may check that next session too. Come to think of it, I am using Windows 7 64 bit and Cubase 7 Elements now, so it’s probably hardware in some way.

Is the sound distorted audibly?
Have you adjusted the waveform view zoom?

the positive part of the soundwave was stronger?
DC offset problem?
Not a long shot but not the only thing either.
Google it, take a glass of water and come back tomorrow :wink:
It’s a command under Audio > process

But if the waveform is already clipped it’s kinda late.

or try iZotope RX2

No, we haven’t noticed any degredation in the sound.

This is not a zoom issue.

In over ten years, I have never seen the positive phase be so much stronger that it clipped only that phase. Besides, the smashed peaks are several decibles lower than the negative peaks. Literally, like the positive phase is hitting a brickwall limiter with a threshold several decibles lower than the negative peaks.

I wouldn’t know where to begin to determine if this could be related to a DC offset. The issue is exactly the same for the preamp and the mics though their circuitry is vastly different. The preamp has its own power supply and the mics run on phantom power.

Thank you all for your input! Our session got cancelled last week due to snow, and this week also, due to Super Bowl, but I’m hoping to try some things next weekend.


This definitely sound like a DC offset problem. It’s usually caused by faults somewhere in the analog circuitry, where the CD power that powers the equipment leaks into the audio signal. In your case it sounds like faulty AD-converters. You should try the following:

a) Record a sinus tone (or use a clean organ sound). Start at the best level (according to your meters) and lower the level while recording. Next, open the recording in the audio editor. See if the waveform becomes more rounded as the recording level decreases. You may only check if the waveform looks unbalanced (it looks like more of the waveform is above the zero-line than below). You may also try selecting “Audio/Process/Remove DC Offset”, and see if the waveform is shifted up or down. And of these will give you a clear indication that you have a DC offset problem.

Since this is a problem with the analog part of the signal chain (digital don’t add DC-offset voltage to the waveform), you need to track down the problem there, by exchanging the parts. Start at the end of the chain and try another DA-converter. If the problem persists, change the next thing (amp or whatever) until you nail down the culprit.

In your case, I guess, the only thing to do is to replace the 828mkII (and maybe the8Pre), to see in the problem persists.