very low mic input since updated to 2.3

[steve]

I just read somewhere - in one of the learned articles online (don't remember which one) that -3dB is ideal.

There is a "scientific" basis for that, though I would phrase it slightly differently.

The facts:
"44100 Hz 16-bit PCM" ("CD quality") is just enough to reproduce the total range of sounds, low to high and quiet to loud, for all practical music listening experience, but there isn't much to spare.

• Human hearing has a range of around 100 dB between "threshold of hearing" and literally "deafening".
• 100 dB is around the maximum dynamic range for 16-bit (a little more with good dithering).
• Digital audio hardware uses integer formats (usually 16-bit integer, or 24-bit integer), so 0 dB is an absolute maximum limit.
• Each "bit" in linear PCM encoded audio is equivalent to 6.0206 dB range (about 6 dB).

In practical terms, it is impossible to record exactly up to 0 dB, so because 0 dB is an absolute limit, and you want to avoid clipping damage, you must aim a little under 0 dB. So long as your maximum peaks are within 6.0206 dB of the upper limit, then you are using a full 15 bits out of the theoretically possible 16 available bits.

Whether your recording peaks at -6 dB or -0.000001 dB does not really matter. You are still achieving full 15-bits dynamic range. "-3 dB" is the mid point within that range. However (and this is important), the closer to 0 dB you aim for, the greater the risk of accidentally clipping and causing permanent damage.


(In professional audio studios, recording is done in "24-bit integer PCM" format, and a recording engineer will typically aim for a peak recording level of around -20 to -12 dB. The bottom (quietest) couple of bits in 24-bit AD converters are just noise, so a peak level of -20 dB gives them a practical range of around 18 bits, which is about 108 dB and loads of headroom.)

[kozikowski]

You can shoot for -3dB goal if you want, but if you do, make sure View > Show Clipping is turned on.

If your presentation has thin red lines anywhere in the blue waves, that means you have clipping (overload) distortion, which for all practical purposes is permanent.



Much better to shoot for occasional peaks at -6dB to -10dB, roughly 50% blue wave peaks.



Koz