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phase reverse on a mic pre

Discussion in 'Pro Audio Equipment' started by perfectwave, Mar 14, 2005.

  1. perfectwave

    perfectwave Guest

    I just purchased the trident s20 dual mic pre, and when i hook up my Neumann 103 it sounds great. One issue is when i push the phase reverse (only running one mono mic) the response seems to change (mostly in the low end). I tried other mics and got the same results. Seems like the condenser mics vary the most. I was just wondering if this is normal, and if it is what causes this difference in the response of a mono source. In my other pre's I get the same charactistics.

  2. perfectwave

    perfectwave Guest

    anyone have any ideas on this?
  3. Kev

    Kev Well-Known Member

    Nov 13, 2001
    no, I don't see this as normal

    seems even stranger

    sorry no ideas at all ... :(
  4. DaveRunyan

    DaveRunyan Active Member

    Dec 13, 2004
    There isn't any difference in sound on any of my mic pres when I change polarity. (as long as I only use one mic) I just checked to make sure.
  5. Kev

    Kev Well-Known Member

    Nov 13, 2001
    I just had a thought.

    this phase switch test ?

    The mic is in a different room far enough away as to not be able to hear the original sound and the source is not just your voice but another voice or guitar etc ..
    and you can hear a difference as you flick the switch ... in real time.

    is this what we are talking about ?
  6. perfectwave

    perfectwave Guest

    im using a Neumann 103 through a trident s20 with headphones....i wonder if my monitors were on whaile i was doing this...good possibility...ill have to go back to the studio and do a retest , make sure my monitors were not on. yeah it was blowing my mind, there was an obivous difference in the bass response even with a 57. huh thad be funny if thats the case...kick myself in the ass if so hahaha
  7. Kev

    Kev Well-Known Member

    Nov 13, 2001
    headphones good
    not perfect but good

    oops ... if the source is your voice then I think you need the monitors off.

    yes please do the test again and don't use your voice but something like the fridge or the heater fan. Run a long lead to another room and get set up in front of your speaker ...
    be careful of feedback as you can still get into trouble as you will be tempted to run a great deal of gain so as to hear inside the fan.
    Double check with headphones.

    please do some sort of test just to settle in your own mind what is going on

    yeah funny
    don't worry about it
    you may have helped someone else learn something
    even so we aren't sure yet that we have found the problem

    if you have an open mind, then there is never a silly question

    let us know how you go !!! ... :cool: :cool:
  8. Kurt Foster

    Kurt Foster Distinguished Member

    Jul 2, 2002
    77 Sunset Lane.
    A 180 degree flip of the phase should not sound any different on a single source, in mono. There should be a difference if you are combining multiple mics on a single pass, especially if you're monitoring in mono.

    First, just to be sure, make sure that all the cables from your mic to the pre amp, from the pre to the recorder are all wired and working correctly.

    Then check the line level cables to your monitor amp and the speaker cables from it to the monitor speakers to be sure they are wired for correct polarity and that alll conductors (particularly if they're balanced line level) are connected.

    This sounds to me like a monitoring issue.
  9. Sebatron

    Sebatron Well-Known Member

    Dec 22, 2002
    The difference is simply due to the fact that you're creating the sound and wearing the headphones ..... consequently there is phase cancellation going on between the headphones and the your voice through the skull.
    If you get someone else to talk into the mics or use a totally external source .... like a fan or whatever .... and remove any possibility of the original leaking into your phones ,,.... that phase switch should not sound sonically different in any position.

    Actually if you record yourself as it is , with it sounding different as you change the switch and talk ,, it should sound ok on playback.
    The cancellation only happens when you wear the phones and do it live.
  10. perfectwave

    perfectwave Guest

    wow never thought about that ...makes sense though...so the lesson from this is if im tracking a vocalist with one microphone, the phase switch can affect the response of his voice in his headphones but only the headphones , not to tape, possibly causing a problem with how he "feels" his voice? interesting ill have to keep an eye on this one.
  11. DanKennedy

    DanKennedy Guest

    Bingo, real nice trick to remember, although to be honest, most people will hear it the same way you do, but it's always worth a flip if the cue mix just isn't cutting it.
  12. Dave62

    Dave62 Guest

    The phase switch will affect the sound monitored live in headphones because the sound is either in phase or out of phase on your eardrums. If you record both and play it back they will probably sound exactly the same in the headphones on playback. I have a thread in this forum about AKG 240 headphones being out of absolute phase from the factory. AKG in Germany confirmed it. The do it for "historical" reasons.
    The cause of the problem is that when you sing your eardrum resonates with your voice from the inside of your head and if your headphone absolute phase is reversed (flipping the mono input phase) it will start to cancel on the eardrum itself. This is volume dependant. I rewired all my AKG headphones to fix this (flipped both speaker leads) but you always have to check. To check, output a recorded 1K tone from your recorder out to the headphones which has one earpiece cupped over the mic and record the tone, it should be the same phase as the original, i.e. the initial wave form should look the same as the first. I own a Central station and the cue output is out of phase with the input...nice.......so you always have to check.
    Another way to check is to record yourself and then quickly play it back thru the headphones, If the sound changes radically, flip the phase and try it again. The "right" phase will be the one that doesn't change.
    I first noticed this when a singer was complaining that the headphones sounded crappy, and he was right.
  13. Kev

    Kev Well-Known Member

    Nov 13, 2001
    sorry guys

    I was trying to be gentle as I had just been accused on another forum of being arrogant and patronising
    so I thought I would get into this answer a little more gentle.

    thanks Seb
    for going more direct than I was prepared to go.
  14. Sebatron

    Sebatron Well-Known Member

    Dec 22, 2002
    Thanks Kev , it's great to see you around here....

    ... and Dan . K . too ! ....

    Legends everywhere. :cool:

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