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I'm quite new in sound recording - I'm only starting out with this as a hobby, and have yet to invest in (most of) the equipment...

Let's say I should record voice with a microphone into a mobile recorder, f.x. Zoom H4N. What are the advantages of connecting a preamp/field mixer, f.x. Sound Devices MixPre-d, between the mic and the recorder? I've understood such a mixer could cancel some clipping if the input levels get too high. Is that right? Does it cancel background noise/humming as well? Does the mixer only simplify the post-processing, or is it essential in making top quality recordings?

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I agree with @JPollock that the built-in mics on the Zoom are fairly good to begin with. What are you hoping to accomplish by using different mics? –  ObscureRobot Nov 14 '12 at 21:57
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@ObscureRobot It's nice to hear its microphones are good - I will probably be using them primarily. It was meant as a general question about when to use a preamp, and I got that answered well. However, I think there could be situations where I wanted other kinds of mics, e.g. a shotgun mic or a wireless lavalier mic, either instead of - or in addition to the internal mics... –  poplitea Nov 14 '12 at 22:43
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2 Answers

Note that the Zoom H4n can record 24 bit samples. If you set your input level so that the loudest sound peaks at half your available headroom, your recording will effectively use 23 bits. That's still plenty of bits left if you plan to downsample to 16bits for your finished product. Unless you are looking for the coloration of a specific limiter or preamp, you are always better off setting your recording levels low and your sample size high.

Also, it should go without saying that you should record uncompressed. SD cards are dirt cheap, so capacity shouldn't be an issue.

Here is why using a 24 bit sample rate helps with headroom. A 24 bit integer has 16,777,216 different values. A 23 bit integer has exactly half that, 8,388,608. A 22 bit integer has 4 million. This is because each bit doubles your resolution. Conversely, if you use only half of your available headroom, then you are only throwing away one bit, not half of your bits. So you could adjust your input so that a peak only uses 1/4 of your headroom, and you'd only be throwing away 2 bits. That leaves you with 22 bits of effective resolution. Still six bits more than CD-quality at 16 bits.

That said, your ADC will probably be more accurate for large sound pressure differences than small. So you don't want to throw away too much dynamic range. But throwing away one or two bits should be fine.

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Thanks for this tip, I haven't thought of that. Highest bitrate and mid-level recording it is! :-) –  poplitea Nov 14 '12 at 22:51
    
Also: experiment. Try different things out. See what works for you. –  ObscureRobot Nov 15 '12 at 2:01
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up vote 2 down vote accepted

The Zoom H4N has built in preamps and microphones.

Preamp is short for pre amplifier. It raises the signal from mic level (very low) to line level so it can be recorded or sent to an amplifier or a signal processing device. One reason you might want to use an external preamp with the Zoom is because it might have a limiter to prevent clipping, or a high pass filter and /or ground lift switch to help with hum.

Personally I just use the built in mics on my Zoom H4N. I don't have an small diaphragm condenser mics of a higher quality than those mics. The Zoom does have a high pass filter built in, which I almost always engage.

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Thanks! Your explanation of a preamp made things clearer to me. Also, it's nice to hear the internal mics are good enough. :-) –  poplitea Nov 14 '12 at 22:55
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