Reduce EM/cell phone jammer noise in voice recording?

[pinky37]

Hi,

I recently purchased DC7 primarily to work on a cassette recording made by my wife, but will also use it in my ongoing efforts to digitive what remains of my LP collection. I've been using other software on this latter project so I'm somewhat familiar with reducing noise on LP recordings, but I'm very much a novice with DC7.

Anyway, back to the issue at hand. My wife is a college student and had to do an interview for a class. She used a cheap, hand-held cassette recorder and it turned our very badly. She tested the recorder ahead of time and it worked fine, then did the interview in the college library. The resulting recording has a LOT of background noise, and not just simple hum or hiss. Since it was made in the college library I have to wonder if they don't have some sort of cell phone jammer going on there, and maybe that's what caused this very loud noise?

The noise is so bad that it often drowns out the voices. My wife has to transcribe this recording and is having a very difficult time with it. I've had some success cleaning this up using a combination of Band Pass, the "1890 Edison 2 Minute White Wax Cylinder" filter with the Keep Residue option, and then the Auto Spectrum CNF Very Aggressive filter. Still, the voices are very hard to understand in much of the recording.

Any suggestions on what to try? What I've done so far is largely trial and error. I thought that Punch and Crunch might offer some help by either bringing out the voices or subduing the noise but haven't had much luck there. Then again, I don't really know what I'm doing. For what it's worth, my wife is interviewing another woman and both have relatively deep voices for women.

Any help would be greatly appreciated. Thanks.

Mark

[Dan McDonald]

Is it sort of random noise like it's going on in the background, or does it have spikes?

If it's fairly constant, then just try sampling a spot with the cnf where they're not talking (even a short segement will do if it's constant).

If it varies, consider using the CNF in one of the modes that changes with the noise levels. Just try clicking on the various options.

If it has spikes, then impulse filters might help.

[cromag]

I frequently record meetings at local schools. My first attempt, using the built in mic on a small cassette, sounded great when I tested it at home, but was a miserable failure at school. Possible reasons would be that I was speaking loudly and clearly, directly into the mic when I tested it at home, in a room with better accoustics -- at school all of the people speaking were much farther from the mic, spread out, and the room was filled with hard surfaces (tables, plastic-and-aluminum chairs, tile floors, metal book shelves, concrete block walls, etc.) and some distant background conversations. Also, the recorder was sitting on a formica tabletop, which probably conducted more of the tape drive noise directly to the mic. Briefly, in the school room the voices were much quieter and the echoes/extraneous noises were much louder.

For subsequent recordings I used an inexpensive microphone on a plastic stand with a short cable to the same recorder. I took the recorder off the table and put it on the floor. These recordings came out much, much better.

As far as cell-phone jamming -- I'm not too familiar with it, but I think it would have to be jamming the radio signal, and I don't think it would affect a cassette recorder. Also, I used to work at a library (a long, long time ago!) and we used tape recorders for transcriptions all the time -- they wouldn't want to jam their own equipment. And I think "jamming" is pretty much illegal -- if not, I've got a few theaters I need to talk to!

[Geebster]

This is just an educated guess, but the noise in the recording may have come from multiple fluroescent lights in the "recording room". Back in the day, I used to work at Radio Shack and when we demonstrated recorders in the store, there was always a lot of noise in the recordings. However, if we were to test the same recorders out in the mall proper, the sound would not be present (the mall I worked in had gas lights in the common area), while our store had the normal fluroescent lighting.... which I don't know if is the case because you really didn't say if the recorder was AC or DC operated. Also, with DC operated, small recorders I have found that they sometimes will pick up noise from the motors within the unit itself.

Like Cromag said, using a dedicated mic should improve the results in the future. The built-in mics in most recorders will not yield the best results.

GB

[Craig Maier]

If it is cell phone type noise, I vaguely recall that there is a preset in the presets sharing area called something like Nortel Noise reducer or something like that. I do know that certain types of cell phones do interfere with audio devices. As a matter of fact, we are presently on vacation in Cape Cod and my wife was playing a cassette tape on our boom box. But, she also put her cell phone right next to the boom box. Every so often, the phone tried to ping the tower and the boom box went nuts producing loud pulsing sounds. This action also erased part of the tape where the cell phone pinged. How could that happen?

Well, if the interfering RF signal from the cell phone was strong enough to forward bias the base to emiter junction of the first audio amplification stage transistor (>0.65 Volts), that would provide rectification and AM detection. Therefore, this dc or low frequency string of pulses would be applied to the playback head and erase the tape in that location, and it did. Moral of the story - - - never leave a turned on cell phone near your tape playback equipment while performing a transfer. You may permanently damage your source material.

Anyway, I am rambeling. Try the Nortel Noise preset and see if that relates to the problem; I am thinking that a jammer might produce signals similar to that of a cell phone itself.

[Craig Maier]

I just found that Cell Phone (Nortel Noise) attenuator in the presets sharing section. Here is the link but I do not know if this will fix your particular problem:

http://www.diamondcut.com/vforum/showthread.php?t=1566

[cromag]

And NPR just had a piece on cell phone jamming. Yep, it's illegal in the states. But, as they mentioned in the write-up, jammers are as cheap and easy to find on the web as "fake V!agra."

[eloyambres]

Generally speaking, different countries have different standards about the legality of cell phone jammer. In America, the FCC, the government agency in charge of the airwaves, has established severe punishment for blocking signals, with the penalty of $ 11,000 and one-year jail for the lawbreakers. However, other countries do not have the strict rules on its usage. France, for instance, turns a blind eye to the blocking signals in the theater. Russia would permit the use of the device in the daily life. China is lax in the enforcement of its restrictions.

[Wallybankes]

Different from other electronics, cell phones have become the necessity of every one's daily life. If someone still has no idea of mobile phones, you must say that "Out!" of course except the senior citizens. To be honest, cell phones really bring us lots of benefits. We use it for talking, sending and playing. With it, our life can be modern one, without it, we will be live in the Mars, you know, know nothing about each other. But do cell phones have no disadvantages? Of course not, more and more people are using cell phones at the cost of other interests. Noises are everywhere, especially the one of mobile phones. What should we do, throw them away? It is a stupid behavior. Have you ever heard cell phone signal booster? It is a new kind of device to solve this problem, effective in blocking the signals of your cell phone and its nearby base station. one side, the mobile phone really benefits us a lot, but another side we also benefit from its noises for a long time, so the fight between the cell phone and cell phone jammer has been a hot topic in society now. Which side you stand by, jamming or not, it depends on you.

[Craig Maier]

The Diamond Cut Forensics Software suite includes a specialized cell phone noise inteference filter.

Craig

[Guest]

Anyway, back to the issue at hand. My wife is a college student and had to do an interview for a class. She used a cheap, hand-held cassette recorder and it turned our very badly. She tested the recorder ahead of time and it worked fine, then did the interview in the college library. The resulting recording has a LOT of background noise, and not just simple hum or hiss. Since it was made in the college library I have to wonder if they don't have some sort of cell phone jammer going on there, and maybe that's what caused this very loud noise? DigitalOceanSiteGroundiPage

[Craig Maier]

If you can send me a short sample of the recording, I can determine the filters and settings needed to reduce the noise. Send it to me at my personal account which is dctools@aol.com

I will then get back to you after the evaluation.

Craig