What is the typical max voltage rms, peak and peak to peak for a sound card line in?

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  • 2
    That depends on your sound-card. – Connor Wolf Jul 16 '13 at 1:50
  • You don't need all three figures requested. Any one of them will tell you the other two. – user207421 Jun 10 '17 at 1:10

Nominal line level for consumer equipment is -10dBV, which is about

$$10^{-10\:\mathrm V/20} = 316\:\mathrm{mV_{(RMS)}}$$

or (for simple sinusoidal waves):

$$\sqrt{2} \cdot 316\:\mathrm{mV_{(RMS)}} = 447\:\mathrm{mV_{(peak)}}$$

or:

$$2\sqrt{2} \cdot 316\:\mathrm{mV_{(RMS)}} = 894\:\mathrm{mV_\text{(peak-to-peak)}}$$

Equipment will often include as much as 20dB of headroom above this before clipping, so a full scale signal could be 10dBV, or 3.16V(RMS), or 8.9V(peak-to-peak).

Of course, no manufacturer wants to be quieter than everyone else, so devices tend to have hotter outputs than they should, and inputs have less headroom than they should. Bend these rules to the extent that you think your customers care more about volume than fidelity.

  • thanks loads. I have a measurement mic with 6 mv output at 94 dB SPL and need to know the gain to use for reasonable input to a sound card at line-in. It is problematical cause when I use MLS/FFT the peak can be very high relative to average SPL. Linkwitz uses a gain of 3x but his mics are more sensitive than mine and are capable of handling 140 dB SPL. Mine crap out lower than that. Also I don't know his following equipment for a comparison. Been thinking of switch ed gain amp with 10 and 20 dB settings not suure if I should also go to 30 dB. – oneoldude Jul 16 '13 at 4:27
  • @oneoldude Well, it's going to depend on what you are recording and your equipment, but professional mic preamps usually have adjustable gain up to 60dB, which accommodates sounds quieter than 94 dB SPL and the higher professional nominal level of 4 dBu. I'd say build your preamp on a breadboard and experiment. – Phil Frost Jul 16 '13 at 12:01
  • I was just testing mike ins on supposedly identical hardware (same model number) yesterday, and the variation in actual input level was HUGE. I suspect there is not the same kind of variation on line level since there is an actual definition on line-level, but it's telling, nevertheless. – Bjorn Roche Jul 16 '13 at 14:51
  • In my experience, inputs still have plenty of headroom because even though everyone wants to be loud, noone wants their inputs to clip when someone plugs a loud device into it. – Bjorn Roche Jul 16 '13 at 14:53

AFAIK, there is no hard standard for that, so it varies by card/chip.

To be on the safe side, I wouldn't go over the 'Consumer audio' level listed on the wikipedia page: http://en.wikipedia.org/wiki/Line_level

Also don't forget that the amplitude of the signal received in the PC depends on the mixer settings. If the relevant mixers are not set to their maximum level, you can still get clipping (or unacceptable distortion) even (far) before the signal received in the PC reaches maximum amplitude, due to limitations in the ADC or its frontend.

If you want accurate signal representation, I would try to locate the datasheet for the chip that your target sound card uses, and stay within the limits listed in there.

  • 1
    I'm not sure the chipset data sheet will help. There may or may not be significant electronics in between. – Bjorn Roche Jul 16 '13 at 2:38

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