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A solution needed for ?gain structure? for recording

Discussion in 'Recording' started by camsr, Jul 19, 2006.

  1. camsr

    camsr Active Member

    Hi, nice forum here. Plan to take some more looks as need be. Anyway, I am using a cassette deck with a microphone input as a poor me's preamp. But I have a problem when I try to record: the voltage or signal level is too high going into my sound card and it clips the A/D converter. I need to find a way to attenuate the signal so its in an optimal range (peaking around -3 to -5dB). I've tried routing through my receiver and using the volume knob to adjust the level, but this added noise on top of the tape deck itself. A teacher at my college mentioned today something about opposing voltages, could this be the way to a possible solution? I'm a newb with electronics but I know how most components work. Would this be a job for a resistor or a more cleverly designed circuit? Thanks for any help you recording gurus can give.
  2. MadTiger3000

    MadTiger3000 Active Member

    Sell all of your extra junk you aren't using, and get an inexpensive preamp.
  3. camsr

    camsr Active Member

    I was thinking an L-pad? Anyone familiar with these?
  4. RemyRAD

    RemyRAD Guest

    camsr, I think the basic problem that you're having is that you are plugging things in to your audio card and don't quite understand how to control levels and manipulate your sound card's built-in mixer control? I assume you are trying to plug it into a general purpose computer that has an on motherboard integrated sound card or an inexpensive "Blaster" type ancillary card? Those are truly horrible, really only good for listening to your MP3 files but their microphone inputs are only appropriate for inexpensive multimedia style computer microphones that require DC power to make the inexpensive condenser element work. You really can't plug anything else into them.

    I actually hope that you are going into the sound card's blue colored " line input" and not that little red microphone input? Those crappy sound cards should not clip when fed into the line input, from a consumer cassette deck. If you are having input level problems, you need to merely adjust the sound cards computer "mixer" to correct the problem. That's called being an "audio engineer" when you play with those volume control thingies. However, you may be adjusting the playback monitor control and not the input recording control? Most inexpensive sound cards have some kind of included mixer application but Microsoft Windows actually includes a mixer that I find more functional in place of those stupid looking included blaster mixers. The cool thing about the Microsoft mixer is that when you first open it, it defaults to the playback monitor mixer. If you go to its " properties" drop-down menu and select "recording", you will now be looking at the input recording control mixer, that's where you want to be. You can then also, if you want to, open up a second instance of the mixer and you will have the playback monitor default mixer also on your desktop. This way you have 2 mixers that you are looking at. One for recording and one for playback monitoring. It's much more simplistic and straightforward to comprehend that way.

    Simply marvelous
    Ms. Remy Ann David
  5. camsr

    camsr Active Member

    Thank you for your input Remy but as you can tell, this is not a digital domain issue. The gain structure of my studio equipment needs to be tweaked so the "blaster" doesn't get overloaded and record a bunch of distorted garbage. Coming straight from a standard RCA output on the cassette deck is just too much for this blaster to handle!!! So, besides a hardware mixer, Im thinking I only got a few options. I hope there is someone here on the recording.org forum that is familiar with electronics and can tell me some other low-cost options for attenuating the input to my card. I have done some searching myself and have found two things that look promising: an L-pad shunt circuit or a transformer-based solution which is more complex and bulkier. A mixer could do this too but I am on a VERY tight budget saving for some other equipment atm so it's out.
  6. RemyRAD

    RemyRAD Guest

    camsr, I really think that you're having some other type of problem because many of my friends have come to me with similar problems with their blaster type sound cards. Most consumer audio devices output a lower line level, such as around .3 volts for a 0 reference level not like normal studio oriented equipment which outputs 1.25 volts. A considerable difference and if you are trying to feed the blaster from a +4DB 1.25 volt output, it will absolutely overload the blaster's line input.

    As you surmise, an " L " pad would be fine. But I really think that you do not have your software mixer recording input control adjusted properly? It's easy enough to make an L pad, especially where unbalanced equipment is concerned. Of course you will need to be handy with a soldering iron. Again I think it's really operator error, sorry. You can also make a variable L pad by going to RadioShack, picking up a dual stereo ganged volume control. I think they have them in 100 K? So all you would have to do than is take the output of your cassette deck, connect the hot side to one side of the 3 terminals of the volume control. Take the ground side and connected to the third terminal of the volume control. Take the middle terminal and connect that to the high side (hot) of the cable going into your sound card. Connect the ground (low side) to the same ground connection on the third terminal. Eh voila'! Do the same to the second channel.

    You see, even though the blasters are really substandard for audio, they're used all of the time in the video editing business since many of the even higher end video editing cards from companies like Avid, Pinnacle (now Avid), Matrox, Conopus and others use the blaster type sound cards as inputs for their editing systems. So I really don't believe for a moment that your blaster is getting that overloaded by a piece of consumer garbage? You are still on a learning curve and I have done this many many times over many years with numerous blaster type sound cards. I don't suspect yours is any exception to the rule?

    Overloaded (I need to lose about 40 pounds)
    Ms. Remy Ann David
  7. dementedchord

    dementedchord Well-Known Member

    $ .02

    hi all... hey man i really think remy's givin it to ya straight.... but if you decide to try the other it would be a mistake to ask for a "L pad" most of the guys in the stores are going to take that as a speaker level pad... you just want a linear taper pot...
  8. camsr

    camsr Active Member

    Problem solved. Turns out it WAS a software problem. I am turning down the level actively by using my receiver to adjust my preamp. But the software I was using before was somehow noiser then what I am using now. Everything works fine now, thanks for the comments.
  9. RemyRAD

    RemyRAD Guest

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