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Preamp tutorial
  • RikerRiker

    As a H4n owner, and coming from a semimusical family, I'm ashamed to ask this question - what are preamps? I don't understand it. If I have my H4n and if I plug my mic into preamp and then connect preamp into zoom, doesn't that mean that I'll feed more noise in the zoom?

  • 5 Replies sorted by
  • Vitaliy_KiselevVitaliy_Kiselev

    Preamp is usually amplifier that has another amplifier after it.

    And usually separtate microphone preamp has much better signal/noise performance than cheap recorders, so no, you do not feed more noise. Idially is just feed line level input into recorder.

  • RikerRiker

    Watching this vid...

    Seems like the guy uses the preamp to preserve the audio from clipping. Isn't that what compressor is supposed to do?

  • Vitaliy_KiselevVitaliy_Kiselev

    @Riker

    SD has good build in limiters. Just check that is limiter on google.

  • bruckerbrucker

    mics alone generate a very low signal so a preamp is required to boost that signal so that it can be heard/recorded.

    the quality of preamps vary depending on the design of the signal path and the components used along the path, which is why some preamps are $10 and can sound like ass and others are a bajillion dollars and yet you might not recognize a difference.

    but because one preamp's design is different to another, they have different sounds as their frequency responses will be different, kinda like how a piece of music can sound different on different speakers.

    for applications like video where you may only be recording on a few tracks this isnt such a big deal, but with music where 12-24 tracks might be a small project, the slightest unevenness in the frequency range gets multiplied across the number of tracks, which can result in muddiness or too much bass or shrilly highs depending on what preamps were used. so you get really flat/clean preamps that are really expensive or you get character preamps that give you a certain sound, which when multiplied adds a bit of mojo to the sound.

    SD make great stuff,.. chunky sounding and a bit warm, but many recordists use them for classical as well so not overly coloured. i myself use SD preamps for both video and audio. great converters as well and very nice limiters as Vitaliy mentioned.

    if your recorder doesnt have a line in you'll be going through the zoom's preamps as well which will add even more colour to the sound so you'd want to set the recording level on the zoom to 0 or as low as it'll go and control gain from the SD or any other preamp.

    a limiter is a compressor with a very high compression ratio and a very fast attack time.

  • DrDaveDrDave

    Preamp is a contextual term, it means different things in different contexts. Audio engineers usually use the term for something that powers a mic and raises the gain to line level so it can be piped into a recorder or other device. Stereophiles use preamps to power amps or record players, and so on.

    Vitaliy's defintion is very good--usually a preamp comes before an amp. But a mic preamp just feeds a recorder in recording work. In live audio, like a show, the preamp can feed an amp as part of the sound system.

    The power supply for the mic can be something called phantom power, or it can be a proprietary type of power. Many of my mics are modified to use use a high voltage preamp, and DPA makes mics that use a higher voltage. Generally speaking, 48 volts is a bit on the low side for a mic but it is a sort of standard. If you aren't an audio nut, stuck with standard voltage.

    Some mics don't need power, and so for these mics, the preamp just supplies gain, and there is usually a switch to turn to Phantom Power off. Some mics use a lower voltage, like 13 volts, and so on.

    Preamps can also match the impedance of the mics by using a switch to change the impedance of the preamp to closely match the mic.

    As a lot of this gear become hybidized, the term "preamp" started to lose clear definition. So for example, my RME FF 400 is a preamp, but it also has AD, DA, a mixer (totalmix) jitter reduction and a whole bunch of other stuff. It still is very loosely called a "pre" even though it is a hybrid.

    A Tascam DR 680 takes this further and combines the pre, the recorder and the DA AD, mixer, limiter, etc in one box.

    Another wrinkle is the new RME box that you can record straight to a USB drive, and there are also "pres" that are firewire or USB interfaces, and a bunch of other types.

    Glazed yet? The term also is used unfortunately for the body of two part mics like the Schoeps CMC6 series, The mic has a capsule and a "preamp" or "preamp body."

    Since you asked about noise, most recordings are noisy and the noise usually comes from the mic. A preamp with a standard (or should be standard) noise floor of -129.5 will not contribute audibly to the noise, but impedance matching may be an issue. A hybrid preamp like the FF 400 is also very quiet, and even the lowly Mackie Onyx has very quiet "pres". Preamps have gotten a lot better over the last five or six years, some of the cheap ones are very good. Hook up a quiet mic to a decent, mid priced pre and you won't hear any noise, or just a trace.

    There is also a lot of cheap junk that isn't very good, and I won't mention any names but I see them everywhere. They either don't publish the noise specs or publish fake ones with confusing terms.

    It must be said that for live video, the ambient noise floor is almost always greater than the the noise floor of the preamp. However, if you screw up the gain, or use a noisy mic, you can get some serious noise. I have no idea why so many recordings are noisy--twenty years ago it was a real challenge to get the noise out, now it is pretty simple.

    Unless it is a tube circuit, the preamp is usually linear from whale to bat, so there is no audible difference in the frequency response. Unlike most things, double blind studies have been done and people can't tell one from the other. However, I do think there is a subtle color associated with pres and converters. The Beyer eight channel pre sounds "dark" and closed". Maybe. But I would not bet that I could pass such a test in a true double blind setup. If you record daily, after a few years you can look back and say, you know RME plus Sennheiser MKH 40, lots of good albums. But it is kind of a guess. The preamps in the Tascam DR 680 are perfectly fine, and the SD pres are not better, they are just in a better case. Which is important if you or your "assistant" drops it.

    And lastly, look for "Class A" preamps. Why not? They aren't very expensive. You can also buy an Audio Upgrades super high speed preamp on a card and bypass whatever pres you have in your box. Instant perfection. (Well, after the solder.)

    I leave all my pres at home and bring the Tascam DR 680.

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