Line-in too hot? Clipping issues...

Discussion in 'Digital Audio' started by millerrh, Nov 5, 2006.

  1. macrumors 6502

    #1
    In trying to record some LPs to my computer, I am noticing that I am getting clipping even though the dB gain is all the way down. My setup is as follows:

    Turntable -> Receiver -> Mac Line In (via receiver's tape out)

    Is my receiver just putting out too strong of a signal? Is there any way around this short of getting some sort of mixer to go in between?
     
  2. macrumors G3

    Sesshi

    #2
    First of all does it sound OK through the speakers?
     
  3. macrumors 6502

    #3
    It's not all that noticeable, but if I increase the amplification just slightly you can really hear the distortion. I'd like to ensure there is NO distortion/clipping when making my recordings. I have software that allows you to see the waveform, so I can visually see where it is clipping. I'd like to get it so that when I do a recording, it is under that max level. Right now I'm thinking the only way to do that is to get a mixer that has an adjustable output.

    That is unless anyone knows of a way to reduce the gain in software before the recording takes place.
     
  4. macrumors 601

    zimv20

    #4
    how exactly are you connecting them?
     
  5. macrumors 601

    zimv20

    #5
    that has to take place in hardware, i.e. before it hits the analog/digital converters. in general, you can use an attenuator (like this one), but i'm not convinced that's solving the real issue here.
     
  6. macrumors G3

    Sesshi

    #6
    So the distortion is happening before the sound hits the Mac? Are you sure you've hooked the turntable up to the correct inputs on the receiver? Is it for the correct cartridge type?
     
  7. macrumors 6502

    #7
    I have my turntable hooked into the Phono jacks. I have an RCA going from my Tape Output jacks on the receiver to my Mac. Most receivers have a "tape out" jack that acts as a feed through for whatever the receiver is currently playing so that you can record it on a cassette player (or computer in my case).

    That accessory you posted was an attenuator for a microphone. What I'm looking for is something for a line level input. Any studio or DJ mixer allows you to adjust the output levels from the mixer. This would do the job of attenuating the signal before it ever got to the computer. And this is what I'm thinking I have to use.

    But you'll notice that you can increase the gain of an input to make it louder when recording (see input volume slider on attachment). That input slider acts as an input gain, not an attentuator. Why not make it quieter also? Is that just not possible? That's what I'm trying to do.
     

    Attached Files:

  8. macrumors 601

    zimv20

    #8
    what *exactly* do you have? your mac doesn't have RCA ins...

    it also works at line level.

    i think there's something going wrong before the signal hits the mac.
     
  9. macrumors 6502

    #9
    The distortion is only due to the fact that it is clipping when recording. It does not distort when I just play the record. But when I record it and play it back, it distorts due to the clipping during recording. I just need to somehow attenuate the input signal and I was hoping to not have to use another piece of hardware to do it.
     
  10. macrumors 6502

    #10
    I have an RCA to 1/8 Y-adapter to go from the RCA cable to the Mac.

    I think what is going wrong is that my receiver has too much voltage on the output RCAs.
     
  11. macrumors 601

    zimv20

    #11
    it's a stereo adapter, yes?

    definitely a possibility. do you have a voltmeter?
     
  12. macrumors 6502

    #12
    Yes, a Stereo adapter. It's the Monster iCable to be exact:
    http://store.apple.com/1-800-MY-APPLE/WebObjects/AppleStore.woa/wa/RSLID?mco=AD2EAFED&nplm=T4504LL/A

    I have a voltmeter and tried to get a good reading. Looks like at the highest point, an individual RCA (i.e. on channel only) was reading 3mV. But that was just using a handheld multimeter and the refresh rate was not very fast.

    So let's just assume that it is running too hot. Is there some sort of way to attenuate the signal using software just like there is to give it more gain? Or does that have to be done in hardware before the signal gets into the Mac?
     
  13. macrumors 601

    zimv20

    #13
    well, according to my Yamaha Sound Reinforcement Handbook (2nd edition), on page 95, i'd expect an unbalanced connection like that to put out around 245 mV.

    regardless, it describes how too low a level can cause distortion and damage your receiver.
     
  14. macrumors 6502

    #14
    It could be that I'm not reading the multimeter or hooking it up correctly. Because based on the information in my audio recording app (and OS X's Input Level display), it is getting too much signal and clipping it. 3 mv vs. 245 mV is rediculously different. I think this must be user error on my part. It's obviously not getting that small of a voltage otherwise I'd be asking how to boost it more instead of the opposite.
     
  15. macrumors 601

    zimv20

    #15
    i'd be looking for mismatches between the tape output and mac input. things like reference levels and impedence mismatches. i don't know much about mac inputs, and apple isn't usually terribly forthcoming in the specs.

    for example, i'm pretty sure your tape outputs are running at -10, unbalanced. if the mac input expects a +4 signal, you're going to need to boost the incoming signal by about 18 dB for everything to match all right.

    i know it seems like the tape output is too much, but what if there's some sort of ALC (automatic level control) on the mac? it may be boosting too much. i have no idea if your mac has ALC, or maybe there's a gain control that does need to be turned down. or maybe you've got the input set to mic.

    which mac do you have and can we find specs for it?
     
  16. macrumors 6502

    #16
    I've got a brand new C2D MacBook Pro. Seems to me (check out the image I posted earlier) that level control IS built into the Mac OS, the problem is that it's only built for increasing the gain, not attenuating the signal. In my audio app that I'm using (Amadeus II), I was able to increase the gain as well and as I used the slider in Amadeus, it also raised the slider in system preferences at the same time (so those two are linked in software).

    I've never heard of any automatic level control. If that really exists, that could be the issue. But due to the fact they give you sliders to increase it, it seems like it wouldn't be automatic. I just wish there was some software filter or something that would reduce the actual signal before it got to the ADC. I bet that would solve my problem.

    Or I could just use an external mixer and adjust the output volume on it...just hoping to avoid that.
     
  17. macrumors 601

    zimv20

    #17
    yes, but it's still post conversion.

    i don't know of any macs that have it, but then again i know pretty much nothing about the one you've got.

    at this point, i'd start the process of elimination. do you have a tape deck? if so, record the phono and see if the levels are okay.
     
  18. macrumors 6502

    #18
    I don't have a tape deck, but I do have another receiver. I hooked everything up to my other receiver with similar results. I'm guessing a "Tape Out" output is higher than what the Mac wants. And the only way is to use a mixer of some sort to reduce that level (which I have done succesfully in the past). I might post a new topic asking who has done a straight LP to Mac conversion and what hardware and software they used.
     
  19. macrumors G5

    CanadaRAM

    #19
    You could google for circuit diagrams to make yourself a simple pad, if you have a soldering iron and a bit of time.
    http://www.uneeda-audio.com/pads/
    http://www.ethanwiner.com/gadgets.html
    http://www.tkk.fi/Misc/Electronics/circuits/line_to_mic.html

    You could use something like the Griffin iMic to input, or a more elaborate USB or Firwire interface that has the capability of taking phono inputs directly (not all do)
     
  20. macrumors 6502

    #20
    Thanks for the advice. I actually own a DJ mixer that I have used to successfully record things like this in the past. So if I have to, I'll just use that to do my recordings vs. solder up my own device (although that might be a pretty cool project). I was just hoping to have a permanent LP to computer conversion thing set up in my bedroom vs. taking my DJ equipment apart or moving my computer every time I want to record an LP.

    So it comes down to this: If I can't do this in software, I have a way around it. I'm curious how everyone else who just records LP's does it now though, cause it seems as though all receivers would output a signal that is too strong for the MBP regular audio line-in.
     
  21. macrumors 601

    zimv20

    #21
    i think most people use this chain:
    LP player -> preamp -> converter -> recording device

    turntables put out a rather low signal. you may want to try putting that through your mixer, instead of the tape out.
     
  22. macrumors 601

    zimv20

    #22
    fwiw, i finally found some apple audio documentation. from the oct 2006 mac book pro section:
    fwiw.
     
  23. macrumors 6502

    #23
    Recording a line-in with Garageband

    I am trying to record a line input using my MacBook Pro's internal sound card and Garageband. The problem I am having is the signal that the sound card is reading is unusually high and is clipping, even when the input volume is turned all the way down. Please see image to see what I am talking about.

    (If this seems familiar, I posted a similar thread the other day, but rephrased it with Garageband since everyone has this software.)

    Does anyone else have this issue when using Garageband (or any other recording application) to record line level stereo signals? The more I play with this, the more I'm worried something is wrong with my sound card.
     

    Attached Files:

  24. macrumors 68040

    Scarlet Fever

    #24
    You can also turn down the line in through system prefs. Have you turned that one down as well? :)
     
  25. macrumors 6502a

    scottlinux

    #25
    Or in Audio Midi Setup.
     

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