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Phase doubt wrt Analog and Digital

Discussion in 'Recording' started by bhuvan, Oct 6, 2004.

  1. bhuvan

    bhuvan Active Member

    I'm not very good at electronics or digital but a doubt came to my head when i was going over some material right now.

    In analog gear, whenever you use an eq etc, you change the phase, backwards or forward, of the voltage or of the current because of what inductors etc do to the signal running through it.

    however, if you use the same device in digital domain, does the 'plug-in' also work on changing the phase of the voltage and current separately, like a set of inductors and capacitors would? The AD process, as far as i know of it now, samples only the voltage changes to convert to bits of digital audio. how does a voltage lag or current lag affect the process of AD and does it make a difference to the sound?

    i've also learnt that the way the phase of the voltage and current components are changed determines how good the device is. since these changes in phase are inevitable, it just matters how it is done. that's why a neve eq sounds better than a mackie eq.

    am i on the right track? also, the digital and AD doubt is bothering me.
     
  2. soundfreely

    soundfreely Guest

    Many plugins are designed in a way to mimick the sound of analog gear (they never really sound the same as analog though). Usually, these plugs are coded in a way that causes similar phase changes in order to help mimick that analog sound.

    As far as the AD process goes, there is usually an a anti-aliasing filter ahead of the sampler. This is a big part of what seperates cheap ADs from expensive ones. That filter is also responsible any possible phasing in the converter. Once the voltages are sampled and multiplexed into a digital word, it is up to software to make phase changes.

    HTH,
    Erik
     
  3. bhuvan

    bhuvan Active Member

    yes erik, plug-ins do mimic the analog circuitry and can't sound the same.

    but like you said and i asked before: the AD process samples and multiplexes the voltage changes of a signal. what happens to the current component? analog components affect the phase of current and voltage separately.

    if the signal turns digital and everything is applied only as voltage changes, what happened to the current?

    my question could really be summed to one basic doubt: once the signal is digital, does it still possess voltage and current as separate components?

    . . . ... and therefore, does a plug-in that mimicks analog, process voltage and current phases separately?
     
  4. soundfreely

    soundfreely Guest

    The converter holds voltage information that will then be converted into a digital word (multiplexing). Once the signal is digital it does not contain seperate voltage and current information. The digital word is a representation of amplitude only. Then your digital signal is comprised only of amplitude (amplitude defined by the word) versus time (the sampling rate). Therefore, a plug cannot truly process the current and voltage seperately, but rather only simulate it.

    Unfortunately, I am getting to the edge what I remember about the digital conversion process. I'll have to see if I can find what I did with my notes and references on the subject.

    Hope this answers your question,
    Erik
     
  5. bhuvan

    bhuvan Active Member

    thank you erik for clearing this doubt.

    well, it seems that since digital can't process V and I separately, that's why it can probably never sound like analog. then it's probably not only about going 96k or 192k or DSD.

    the other thing that i'm thinking about is that it's the current ultimately that drives the voice coil, so if the cumulative phase output of that has been ignored by a whole segment, that's a big fault.

    things making more sense now. thanks!
     
  6. Kurt Foster

    Kurt Foster Distinguished Member

    I am going on memory here but I remember reading that some eq plugs (most) do affect phase .. but some other eq plugs (the more expensive ones that use a lot of computing power) do not affect phase ...
     
  7. soundfreely

    soundfreely Guest

    Supposedly, linear phase EQs do not affect phase.

    -Erik
     
  8. Steve Halko

    Steve Halko Guest

    We're mixing a few things up here. Phase actually describes the relationship between TWO things.

    Here are some examples:

    1. Phase can describe the relationship between a voltage waveform and a current waveform (e.g. - the voltage leads the current in an inductor)

    2. Phase can describe the realtionship between an input waveform and an output wavform (e.g. - the transfer function of an EQ)

    3. Phase can describe the realtionship between two input waveforms (e.g. - the signals from two microphones placed at different distances from a guitar amplifier)

    An EQ plug-in might be designed to be linear phase, or it might be designed to mimic the phase realtionship in an analog EQ (see #2 above). But this has nothing to do with #1 above - we usually don't care about the current waveform in a digital system.
     

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