Horrible pops after mixdown - help! :(

Hello.

I don’t know much about computer audio recording but I was just using n-Track Studio to have some fun and a friend and I recorded a little Beatles tune. The individual tracks came out quite nicely, even if a little badly recorded, and then the whole thing went from bad to worse.

Apparently, once I apply one of the effects to a .wav file, the .wav file immediately gets these horrible clicks and pops at various position throughout its length. Then, when I mixdown the tracks, the places where the “blemishes” were sound twenty times worse. I really can’t describe the sound, so I have put up a small sample of it and am also including here a screenshot of what the error looks like in Audacity.

In particular, I used the Reverb effect on all tracks (three in this case), if that makes any difference. Oh, and I also watched for clipping. I didn’t see any! I must assume the applied effects are somehow creating these pops and blips in the wav files (especially where the wav file already had one in the first place, albeit a very small one), and then this becomes dramatically pronounced after mixdown.

If you could please tell me how I can at least mix down these three wavs together without them sounding so horrible I’d be very grateful. It’s just goofing around but I spent enough time on it. Would be nice to have a halfway listenable version of it. :)

The error looks like this (61kb jpeg file):
http://www.angelfire.com/ny3/darkestdays/audacity.jpg

And it sounds like this (1.78mb wav file).
http://www.angelfire.com/ny3/darkestdays/sample.wav

Thank you!

When I tried to listen to your file I got the following message:
"Angelfire does not allow direct linking
from offsite, non-Angelfire pages,
to files hosted on Angelfire."

Try increasing playback and record buffer sizes (on the menu click file -> settings -> buffering settings) , and make sure that you don’t have any background processes like anti-virus software or messenging running while you record.

T

Hi, Tspringer. I should have thought of the hotlinking thing. I’ve linked it through an .htm page. Here:

http://www.angelfire.com/ny3/darkestdays/sample.htm

Please be aware Angelfire will give you one pop-up.

I should also add something. The “pop” you will hear (it’s more like a “twisting” of the sound than a pop) was actually originally a small “blemish” as I first recorded the track into n-Track. But it was hardly noticeable. It was the use of the effect that made it sound so bad.

But I will follow your advice and increase the buffer limits. Let’s see if I get similar problems in the future.

More/bigger buffers? ???

On some sytems, many small buffers works best, on other systems, a few large buffers works best, even though the overall latency is the same.

Experiment, but the important thing is more buffering. :)

I had a quick view of the posted wave file in an editor. This looks like a bad DC offset to me. This could be caused by some malfunctioning piece of hardware, or introduced by a plugin getting confused by the DC offset in the signals sent to it. Try examining the track(s) for even a slight DC offset, and check back on the signal chain to find the culprit. It could be a ground lift, or a DC signal introduced by a faulty connection somewhere. I think Audacity has a DC compensation function you could try to use if the tracing of the cause leads nowhere.

regards, NIls

I think that Nils might be right. When I finally got to listen to the sample, it didn’t sound like what I normally hear when I get buffer over/under runs. If he is right, the first thing to do would be to make sure that all the power supplies for your audio equipment are grounded at a single point (eliminates ground loops). You can accomplish this by plugging everything into a single multiplug strip which is plugged into the wall outlet.

Nils, thanks for pointing out that function in Audacity.

T

I finally had the chance to do a closer study of the wave file. This is definitely a DC surge of some sort - and one mean one, too. It suddenly jumps to FSD (full scale deflection - highest digital value possible) and stays there for about half a second before falling slowly down again. The caps on the sound card probably took a great part of the strain. This might originate from a motor starting, e.g. a refrigerator pump, or maybe something turned off, or on, during the mixdown procedure. A lightning striking the power cables in the vincinity of your home may also trigger such an event, but this usually makes the PC restart - or refuse to boot up at all. You made a real-time (i.e. not an offline) mixdown, right?

I strongly suggest that you examine your cablings - and that you do it NOW! If you leave things alone, and you are lucky, then your soundcard will probably suffer an untimely demise. If you are less lucky, you might get fried(!) yourself… If you suspect something is fishy about the electrical installations in your home, get a qualified eletrician to look things over and correct whatever faults there may be.

I know, this will cost you time and money, and you would rather spend your money on new gear and your time making music, but you will make that much better music knowing that your equipment is safe to use, and won’t fail when you least expect it.

I didn’t mean to frighten you, but better safe than sorry…

regards, Nils

Let me add one thing to Nils comments: One thing that can cause amazingly large voltage spikes is turning on a fluorescent light that has a failng balast. If there is a fluorescent light on the same circuit as your computer, make it one of the first things that you check. I was once working in a lab setting where I was using a specially designed circuit that went bonkers every morning. Finally I realized that it happened every time the fellow in the office next to mine arrived. I asked him what his routine was each morning. This included turning on his fluorescent desk lamp. His office and the lab shared the same circuit. Got him to ditch the lamp - problem solved.

T

endorphine will cause DC offset problems. If that is being uses try removing it and see if the problem is less. Though DC offset doesn’t “sound” like anything, it can cause peaks that otherwise aren’t over the 0 db limit to be clipped. It’s my guess that’s what’s happening. Anyway, if endorphine will do it so will other plug-ins.

As mentioned, if any on the tracks had DC offset it can be amplified at mixdown making the problem much worse.

Get this — http://www.analogx.com/contents/download/audio/dcoffset.htm