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how the microphone preamp impedance affects the microphone sound.

I am researching some possibilities to get more gain from my dynamic microphone input, and for now, I will probably buy the Alctron microphone preamp. But I am still trying to understand what the impedance adjustment is for, and what difference it makes if the preamp's impedance is higher or lower than the microphone's. My microphone is a Shure SM 58, which has 300 ohms, and the Alctron MA-1 has 150 ohms. However, there's the Alctron MA-3, which has a switch to select the impedance value (even though it doesn’t have exactly 300 ohms, it has 150 and 350 ohms options on the switches). I'm wondering if it’s worth buying it or if the MA-1 would already solve the problem.

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Comments

  • wimwim
    edited September 2

    Why is it a problem? You’re recording to a digital, not analog device. Analog recording principals don’t necessarily apply. Why not just boost it after input?

    (Btw, it’s a sincere question. I don’t know a lot about the subject.)

  • edited September 2

    With somewhat modern interfaces there's no need record crazy hot unless there's absolutely no way to digitally adjust the level.

    For a HOT digital signal it's better to look at the interfaces line-up level (ie. maximum input level).

    As an example my Audient ID4Mk2 has a 58db gain-range and a 12db line-up level which gives an effective 46db of gain if 0dbFS is the 'target'.

    The SSL2 on the other hand has a 62db 'gain range' but a 5.5db line up level which gives an effective gain of 56.5db. (10.5db higher than the ID4Mk2).

    The Focusrite 2i2 4th gen has a line-up level of 16db and a gain-rage of 69db giving it an effective gain ~3.5db lower than the SSL2.

    Before I knew better I bought the SE Electronics DM-1 dynamite (extra 28db of gain) to boost the levels but in reality I don't need it and it even increases the noise by a few db compared a recording without a DM-1 boosted to the same level.
    (The DM-2 allows change of gain (15/30db) as well as adjusting the impedance).

    Depending on what is being recorded the SM58 might not be the right mic if an insane amount of gain is needed to reach a proper recording level.

  • If the impedance of the mic and the preamp match, you will have an optimal signal transfer. Any mismatch (higher or lower) will result in some loss of signal. It is correct that you can just crank up the preamp to compensate for this. The disadvantage is that this can lead to more noise from the preamp.
    The best way for you would probably to just experiment and see if the noise is negligible. Or check on the web if anyone is using some of the mic / preamp combinations you consider.

  • If I'm not mistaken the impedance of the input should always be higher than the source so it won't overload the circuit.

  • @Samu said:
    If I'm not mistaken the impedance of the input should always be higher than the source so it won't overload the circuit.

    Agreed, except if you have an input transformer, in that case the impedances should be 1:1 indeed.

  • @rs2000 said:

    @Samu said:
    If I'm not mistaken the impedance of the input should always be higher than the source so it won't overload the circuit.

    Agreed, except if you have an input transformer, in that case the impedances should be 1:1 indeed.

    I've read somewhere that for the SM58 (Which is the mic in question here) the recommendation is to have a 1:10 ratio, so ~3000 ohms for the input the mic is plugged in to should be more than sufficient.

    The Mic specs also report the output impedance for 1 specific frequency (1k) and it varies heavily across the frequency spectrum.

    From what I can see from the specs of the Alctrons they are somewhat similar to the DM-1 which I have.
    I'd say that if someone needs more than say >50db of gain for a SM58 the it's the wrong mic for the job.

    The Lewitt Connect 6 has plenty of gain but the SM58 was not made for things like asmr one meter away from the microphone :sunglasses:

  • @tchem said:
    I am researching some possibilities to get more gain from my dynamic microphone input, and for now, I will probably buy the Alctron microphone preamp. But I am still trying to understand what the impedance adjustment is for, and what difference it makes if the preamp's impedance is higher or lower than the microphone's. My microphone is a Shure SM 58, which has 300 ohms, and the Alctron MA-1 has 150 ohms. However, there's the Alctron MA-3, which has a switch to select the impedance value (even though it doesn’t have exactly 300 ohms, it has 150 and 350 ohms options on the switches). I'm wondering if it’s worth buying it or if the MA-1 would already solve the problem.

    What is the situation for which you are trying to get more gain? Are you plugging the mic into a mixer or an audio interface? What mixer or interface? What are you recording?

  • You got perhaps 4 of the 10 most serious players on here attention. Now I’m curious,

  • I will use it for live shows. I have a metal band, and I’ve noticed that many times when the venue's equipment isn't very good, it would be useful to have a clean gain boost instead of turning up the venue's mixer too much, which often causes sound issues. I like to sing at a low volume, especially depending on the type of screamo I’m using, so I think a preamp would be very useful. The question is, if I buy this Alctron MA-1, which has a lower impedance than the microphone, would the sound be bad or not, considering there's no way to test it beforehand

  • @tchem said:
    I will use it for live shows. I have a metal band, and I’ve noticed that many times when the venue's equipment isn't very good, it would be useful to have a clean gain boost instead of turning up the venue's mixer too much, which often causes sound issues. I like to sing at a low volume, especially depending on the type of screamo I’m using, so I think a preamp would be very useful. The question is, if I buy this Alctron MA-1, which has a lower impedance than the microphone, would the sound be bad or not, considering there's no way to test it beforehand

    To be totally honest it's a total waste of money, the noise-floor of the venue (during performance) is likely at the level where you won't be even able to notice the difference once everything is properly set up.

    If the venue has a sound technician (which any serious venue should have!) ask him/her for advice!

    The PA should be able to easily handle a SM58 it's as 'standard' as they come and apply eq and compression to the vocals to lift them up a notch.

    I've only got experience dealing with the Allen & Heath DLive consoles/systems and those provide at least 60db of analog low-noise gain and an additional 24db trim (After AD conversion) if/when needed with proper filtering/eq, noise-gates, compressors/limiter with addition make-up gain per channel, all this is with more than enough system gain to make a soft asmr performance blow out the ears of the audience...

    So I'd say it's more important to talk the venue technician than try to solve the problem on your own.

    That's just my stance, others may have different opinions...

    Cheers!

  • @tchem said:
    I will use it for live shows. I have a metal band, and I’ve noticed that many times when the venue's equipment isn't very good, it would be useful to have a clean gain boost instead of turning up the venue's mixer too much, which often causes sound issues. I like to sing at a low volume, especially depending on the type of screamo I’m using, so I think a preamp would be very useful. The question is, if I buy this Alctron MA-1, which has a lower impedance than the microphone, would the sound be bad or not, considering there's no way to test it beforehand

    It is highly unlikely that the mix problems are related to the levels they are receiving from your mic. Any pa will have preamps capable of handling it. It sounds like lack of attention from whoever is handling the sound.

  • wimwim
    edited September 2

    I'm having a good laugh picturing anyone in a metal band being successful in getting everyone else to turn their levels down a bit. But that's the real correct solution. 😂

    More'n likely boosting the signal will just result in the house lowering the vocal gain at the mixer. Seems like this is fixing the wrong problem here. But what ya' gonna do?

  • I understand that it might not be the best solution, but I thought about this because there isn't always a good sound technician. Usually, when I ask them to add a compressor and such, they end up setting it up incorrectly, which only makes things worse. That's why I'm putting together a setup where I can control the reverb and delay on my vocal pedal myself, so I can set it up the way I want. And regarding compression, sometimes the mixer isn’t digital or of high enough quality to have it, so having the microphone output with more gain could be helpful. But I agree, it's kind of an unnecessary piece of equipment; it would be more of a test for cases where the equipment is really bad. I'm playing every week, and there are venues where you don't need anything; the equipment is good quality, and the sound technician is skilled. But there have also been some specific situations where it’s exactly the opposite, so maybe this could help.

    It would be more of a piece of equipment to have on hand in case I feel like the vocals are a bit dull. But then comes the question of how much this impedance difference would affect the sound or not. I think I’ll only find out by testing it.

  • Cue the guitar player(s) showing up here to ask about guitar pickup signal boosters. 😂
    Sorry, I'm just having some fun being annoying. I'll go away now.

  • @tchem said:
    I understand that it might not be the best solution, but I thought about this because there isn't always a good sound technician. Usually, when I ask them to add a compressor and such, they end up setting it up incorrectly, which only makes things worse. That's why I'm putting together a setup where I can control the reverb and delay on my vocal pedal myself, so I can set it up the way I want. And regarding compression, sometimes the mixer isn’t digital or of high enough quality to have it, so having the microphone output with more gain could be helpful. But I agree, it's kind of an unnecessary piece of equipment; it would be more of a test for cases where the equipment is really bad. I'm playing every week, and there are venues where you don't need anything; the equipment is good quality, and the sound technician is skilled. But there have also been some specific situations where it’s exactly the opposite, so maybe this could help.

    It would be more of a piece of equipment to have on hand in case I feel like the vocals are a bit dull. But then comes the question of how much this impedance difference would affect the sound or not. I think I’ll only find out by testing it.

    Just to check, do these venues definitely not have mixers with separate gain and volume controls? I think most mixers have that. If they do, increasing the gain on your channel before increasing volume should be enough. If they don't, you might be better getting your own mixer for the band. Or are the rest of the guys all just using amps rather than going through the PA?

  • edited September 3

    @Gavinski said:

    @tchem said:
    I understand that it might not be the best solution, but I thought about this because there isn't always a good sound technician. Usually, when I ask them to add a compressor and such, they end up setting it up incorrectly, which only makes things worse. That's why I'm putting together a setup where I can control the reverb and delay on my vocal pedal myself, so I can set it up the way I want. And regarding compression, sometimes the mixer isn’t digital or of high enough quality to have it, so having the microphone output with more gain could be helpful. But I agree, it's kind of an unnecessary piece of equipment; it would be more of a test for cases where the equipment is really bad. I'm playing every week, and there are venues where you don't need anything; the equipment is good quality, and the sound technician is skilled. But there have also been some specific situations where it’s exactly the opposite, so maybe this could help.

    It would be more of a piece of equipment to have on hand in case I feel like the vocals are a bit dull. But then comes the question of how much this impedance difference would affect the sound or not. I think I’ll only find out by testing it.

    Just to check, do these venues definitely not have mixers with separate gain and volume controls? I think most mixers have that. If they do, increasing the gain on your channel before increasing volume should be enough. If they don't, you might be better getting your own mixer for the band. Or are the rest of the guys all just using amps rather than going through the PA?

    Sure they do, but you never know what signal quality arrives at the mixer inputs with all kinds of mis-treated, loong multicore cables out there, probably with bad connectors, bad shielding etc.
    A preamp might indeed reduce the noise levels in such cases.

    @samu Are you talking about 1:10 impedance ratio between mic and transformer or 1:10 transformer ratio? 😉

  • @wim said:
    Cue the guitar player(s) showing up here to ask about guitar pickup signal boosters. 😂
    Sorry, I'm just having some fun being annoying. I'll go away now.

    But you do make a good point about where to make gain adjustments, as gain staging is what should be considered rather than make the source as loud as possible.

  • @rs2000 said:

    >

    @samu Are you talking about 1:10 impedance ratio between mic and transformer or 1:10 transformer ratio? 😉

    Input impedance on the console/mixer :sunglasses:

  • @tchem said:
    I understand that it might not be the best solution, but I thought about this because there isn't always a good sound technician. Usually, when I ask them to add a compressor and such, they end up setting it up incorrectly, which only makes things worse. That's why I'm putting together a setup where I can control the reverb and delay on my vocal pedal myself, so I can set it up the way I want. And regarding compression, sometimes the mixer isn’t digital or of high enough quality to have it, so having the microphone output with more gain could be helpful. But I agree, it's kind of an unnecessary piece of equipment; it would be more of a test for cases where the equipment is really bad. I'm playing every week, and there are venues where you don't need anything; the equipment is good quality, and the sound technician is skilled. But there have also been some specific situations where it’s exactly the opposite, so maybe this could help.

    It would be more of a piece of equipment to have on hand in case I feel like the vocals are a bit dull. But then comes the question of how much this impedance difference would affect the sound or not. I think I’ll only find out by testing it.

    I don’t think you need more output, it’s pretty much irrelevant if it’s going to a FOH console, sound tech, etc… Ultimately it’ll be the sound tech who will decide on the levels. He can pull the guitars down a notch to let the vocals through, eq to separate, etc… or not.
    Not having your own sound tech you’re pretty much sold. It’s frustrating but you just have to trust them.
    There’s some important things you can do to have more control. I’d focus on this:

    That's why I'm putting together a setup where I can control the reverb and delay on my vocal pedal myself, so I can set it up the way I want.

    There’s a ton of options but something like a Voicelive3 by TC Helicon (there’s probably newer stuff, that’s just the one I own and I love it) will help you control the specific sound you’re after. Importantly, you can change the sound for each song, song part, etc… more reverb here, a lot of delay there, some distorsión here to cut through…
    One of the most important factors to consider when you’re in the hands of an “external” sound guy is that they don’t know the songs and dynamics. Their priority will be (rightfully) to avoid feedback which means that you’ll be probably lower than you should during quieter parts. Having your own presets and sound from a pedal will help with this as, if done right, you’ll have a more consistent signal to the console.
    I only started using amp-sim pedals at the (so far) end of my “stage career”, I wish they had come up sooner. If you don’t have your own sound tech I’d go for controlling as much as I can from source, but don’t get caught up in impedance or any of that, go for the big stuff.

  • edited September 3

    @tahiche said:

    @tchem said:
    I understand that it might not be the best solution, but I thought about this because there isn't always a good sound technician. Usually, when I ask them to add a compressor and such, they end up setting it up incorrectly, which only makes things worse. That's why I'm putting together a setup where I can control the reverb and delay on my vocal pedal myself, so I can set it up the way I want. And regarding compression, sometimes the mixer isn’t digital or of high enough quality to have it, so having the microphone output with more gain could be helpful. But I agree, it's kind of an unnecessary piece of equipment; it would be more of a test for cases where the equipment is really bad. I'm playing every week, and there are venues where you don't need anything; the equipment is good quality, and the sound technician is skilled. But there have also been some specific situations where it’s exactly the opposite, so maybe this could help.

    It would be more of a piece of equipment to have on hand in case I feel like the vocals are a bit dull. But then comes the question of how much this impedance difference would affect the sound or not. I think I’ll only find out by testing it.

    I don’t think you need more output, it’s pretty much irrelevant if it’s going to a FOH console, sound tech, etc… Ultimately it’ll be the sound tech who will decide on the levels. He can pull the guitars down a notch to let the vocals through, eq to separate, etc… or not.
    Not having your own sound tech you’re pretty much sold. It’s frustrating but you just have to trust them.
    There’s some important things you can do to have more control. I’d focus on this:

    That's why I'm putting together a setup where I can control the reverb and delay on my vocal pedal myself, so I can set it up the way I want.

    There’s a ton of options but something like a Voicelive3 by TC Helicon (there’s probably newer stuff, that’s just the one I own and I love it) will help you control the specific sound you’re after. Importantly, you can change the sound for each song, song part, etc… more reverb here, a lot of delay there, some distorsión here to cut through…
    One of the most important factors to consider when you’re in the hands of an “external” sound guy is that they don’t know the songs and dynamics. Their priority will be (rightfully) to avoid feedback which means that you’ll be probably lower than you should during quieter parts. Having your own presets and sound from a pedal will help with this as, if done right, you’ll have a more consistent signal to the console.
    I only started using amp-sim pedals at the (so far) end of my “stage career”, I wish they had come up sooner. If you don’t have your own sound tech I’d go for controlling as much as I can from source, but don’t get caught up in impedance or any of that, go for the big stuff.

    I used to perform live quite a lot when I lived in China (acoustic guitar and vocals, sometimes solo, sometimes with bands), often at commercial gigs where the people hired to do the sound had good gear but basically didn't have a clue how to use it. If you often encounter subpar sound guys, the only sane approach is for you or someone in your band to learn the ins and outs of tweaking your own sound ASAP, otherwise it will be very hard to enjoy playing live. You mentioned in your first post that the equipment often isn't good. That might be true but bad sound guys are a far more common problem. If equipment really is the issue, is it really the mixer or is it the speakers etc? If the equipment is really the problem, you might want to buy your own but then you or someone in the band will really need to know how to use it and how to mix a band, otherwise it won't solve the problem. If money is an issue, maybe find someone who knows what they're doing and pay them to teach you, as you're unlikely to be able to afford your own sound guy.

  • One thing that is very often overlooked is proper communication between the act and the sound-tech about the sound the act wants produce and always do a proper sound-check before it's time to perform.

    As an example it's a good start if vocalist to really knows how much compression and eq their own voice needs especially if they are used to a specific microphone and really communicate that to the sound-tech, all serious sound-tech guys know hot to dial in the console for the specific venue, granted if it's some really old crap gear that has zero tweaking abilities I'd say avoid those venues if absolute control over every sound detail is important.

    One common problem is also that everyone on stage wants to hear them selves louder (especially when using loud stage monitors instead of in-ears) than the other and don't give a sh*t about how it sounds in the ears of the audience :sunglasses:

    Proper communication is more than likely needed to solve the issues popping up at various venues.
    The more the information the sound-guys get prior to the acts appearance the better.

    As for reverb in general, depending on the size of the venue wrong settings can totally f*ck up the vocals...

  • @Samu said:
    One thing that is very often overlooked is proper communication between the act and the sound-tech about the sound the act wants produce and always do a proper sound-check before it's time to perform.

    As an example it's a good start if vocalist to really knows how much compression and eq their own voice needs especially if they are used to a specific microphone and really communicate that to the sound-tech, all serious sound-tech guys know hot to dial in the console for the specific venue, granted if it's some really old crap gear that has zero tweaking abilities I'd say avoid those venues if absolute control over every sound detail is important.

    One common problem is also that everyone on stage wants to hear them selves louder (especially when using loud stage monitors instead of in-ears) than the other and don't give a sh*t about how it sounds in the ears of the audience :sunglasses:

    Proper communication is more than likely needed to solve the issues popping up at various venues.
    The more the information the sound-guys get prior to the acts appearance the better.

    As for reverb in general, depending on the size of the venue wrong settings can totally f*ck up the vocals...

    Oh yeah, proper monitors and positioning of said monitors is so important too

  • @Samu said:
    One thing that is very often overlooked is proper communication between the act and the sound-tech about the sound the act wants produce and always do a proper sound-check before it's time to perform.

    ...and unfortunately it seems to be quite common that "sound techs" don't have a good reference sound in mind to aim at. They have all the gear today but often struggle to use it correctly. Some don't even walk around the venue to get an idea of the sound at different listening positions and some give us a boomy mess instead of tight bass.

  • @tchem said:
    I am researching some possibilities to get more gain from my dynamic microphone input, and for now, I will probably buy the Alctron microphone preamp. But I am still trying to understand what the impedance adjustment is for, and what difference it makes if the preamp's impedance is higher or lower than the microphone's. My microphone is a Shure SM 58, which has 300 ohms, and the Alctron MA-1 has 150 ohms. However, there's the Alctron MA-3, which has a switch to select the impedance value (even though it doesn’t have exactly 300 ohms, it has 150 and 350 ohms options on the switches). I'm wondering if it’s worth buying it or if the MA-1 would already solve the problem.

    Can you post your SC?

  • Sorry, what is an SC?

  • Often, the sound technician doesn't even have time to worry about details. We arrive at the venue and have very little time to set everything up, which is why I'm concerned about having some things ready to go. But anyway, I bought the Flamma Fv01 microphone pedal, which already has a preamp, some reverb options, delay, two forms of equalization, and a pitch correction that can be set very subtly. I think it will be a good addition to the setup.

    Thank you all for your comments; they made me consider some details. Now, as for the compressor, I just need to get in sync with the venue's sound technicians.

  • @yellow_eyez said:

    @tchem said:
    I am researching some possibilities to get more gain from my dynamic microphone input, and for now, I will probably buy the Alctron microphone preamp. But I am still trying to understand what the impedance adjustment is for, and what difference it makes if the preamp's impedance is higher or lower than the microphone's. My microphone is a Shure SM 58, which has 300 ohms, and the Alctron MA-1 has 150 ohms. However, there's the Alctron MA-3, which has a switch to select the impedance value (even though it doesn’t have exactly 300 ohms, it has 150 and 350 ohms options on the switches). I'm wondering if it’s worth buying it or if the MA-1 would already solve the problem.

    Can you post your SC?

    Sorry, what is an SC?

  • Signal Chain maybe?

  • Soundcloud.

  • Regarding the issue of impedance, here follows a brief explanation of the main problems arising from Impedance Mismatch in microphones.

    1) High Input Impedance - Weaker Signal; Increased Noise; Loss of Detail.
    If the input impedance of the equipment (such as a pre-amplifier, audio interface, or mixer) is very high compared to the output impedance of the microphone, the signal may be weak or attenuated. This occurs because the microphone cannot adequately drive the equipment's input, resulting in a lower signal level. To compensate for the weak signal, you may need to increase the gain on the pre-amplifier, which can introduce additional background noise into the audio signal. In addition to the increase in noise, this situation may cause a loss of detail in the high frequencies, affecting the clarity and fidelity of the sound captured by the microphone.

    2) Low Input Impedance - Distortion; Loss of High-Frequency Signals; Alteration of Frequency Response.
    If the input impedance of the equipment is very low compared to the output impedance of the microphone, the microphone may have difficulty "pushing" the signal to the equipment, which can result in distortion. This distortion can occur because the microphone cannot provide the necessary current to "feed" the low impedance input. A very low input impedance can cause attenuation in the high frequencies, resulting in a muffled or dull sound. The mismatch can alter the overall frequency response, resulting in a sound that does not accurately represent the original signal captured by the microphone.

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