Wave forms look assymetrical - explanation.

The waveforms drawn in the edit window of LE 5...sometimes look assymetrical. That is to say, the plus and the minus do not look symmetrical. Does this point to phase cancellation. If not what does this visual shape mean in the aural world?

There must be something horribly wrong with your system. All my sound waves are perfectly symmetrical! Sounds don't wait for the 'end of a wave' to change character, and transients are intantaneous and non-uniform.

My favorite waveform is a real trumpet, It looks like a corrupt file!

Maybe you have "Draw Waveforms Rectified" enabled in the Display preferences? Targon

All jokes aside. I dont have the waveforms rectified. My question was directed at the curious situation where there is a greater amount of positive than negative in each "bunch" of sound as drawn by the waveform (eg: a tape ID announcement for example, many times shows more positive than negative on for each syllable). Other waveforms are fine they look symmetrical. They are not of course. It depends on the the zoom. But a 1 second min/sec scale (ie in slip/shuffle the basic grid is a 1 second chunk) "assymetrical" waveforms are quite common. Does anyone have a technical understanding of the acoustic and or electronic causes of this? Seeya

Quick search summary. DC offsets major probs. Editing pops. Headroom reduction. Soaking up bandwidth in mix. By the way... I do a DC offset as standard practice on all my track using the standard LE plug. Is this plug as good as it gets for DC removal? Question: If two files are used on one track and the DC offset is different for each will the Protools DC offset removal plug do the job for both? I suppose it would if they were still separate files. But what if they are one file. Another example. Multiple mics and amps used to create an analogue stereo mix (say a band of 5 players using 24 channels to mix to stereo). The 2 track analogue tape is digitised and mastered in PT LE 5.????. What if all those different channels had a differing level of DC offset. I suppose the PT plug has to do a bit of fancy averaging arithmatic. Is this the case?

Like I said, my knowledge in the area is limited...but..I'll do the best I can. Yes, the DC offest plugin can analyze both sides of a stereo file and correct one or both sides as needed. A soundwave is like AC...it oscillates back and forth (or..up and down). In the middle is a zero constant...(the middle or average of the up to down point). This is the DC offset. DC offset is a constant....a straight line. When you have a DC offset problem...this line no longer is at zero...but shifted to someother constant usually..below zero. So, its not like the problem is intermingled with your soundwaves...its more like a shift problem. finding zero point is easy...its the length of the amplitude of the sine wave divided by 2. The way to check to see if any of your gear is causing it...would be...to place a mic in a soundbooth...and record silence. You should have a straightline. Check to see that the straightline is ON zero..not above or below. The idea is....to take care of the problem on the front end...not the backend. It happens sometimes...as with DSP effects. But...if your recording everything with DC offset....I'd suggest you get to the root of it..in your gear....before I would worry about how good the DC offset removal plug is. Here are the most common causes DSP settings Ground problems with gear/cabling Anything that could introduce voltage into the line...like a bad capacitor somewhere. Old amps...etc. So step one would be...to record dead air with no effects...and see if it records to zero. Next...record input from your board..or other equipment as source ...but record silence...and see if you can locate which are your problem is coming from. From there....once the equipment is located ....check cabling and ground issues...and if its a dsp unit...check settings. .if you have a voltage feed into one of your lines...its feeding a constant signal or offset into every track. Some plugins can actually...analyze and correct DC offests as you record. I think the deal is...to try and get rid of the problem up front.. Again..the most common cause is mal settings of DSP gear. If you have any outboard DSP gear...you might want to double check your settings. If you are using plugins on your recording tracks...take them off when you do the tests. sorry, wish I could help more but thats about the limit of my knowledge. dcornutt

No apologies necessary. Very helpful Mr D Cornutt - as usual very clear writing and systematic thought. Your help is much appreciated on this list. Thanks. Mark