common path assign?

Discussion in 'Microphones (live or studio)' started by redface, Oct 17, 2006.

  1. redface

    redface Guest

    what is a common path assign for a signal known as? What are the bus in and outs on a console for?
  2. cusebassman

    cusebassman Active Member

    Sep 13, 2006
    I think the standard terminology for the signal path in whatever broad terms you're talking about is called the "signal chain". This is the phrase I've seen most often when people are referring to the path through which the signal flows, mainly in reference to a complex system. I've never read any posts or articles where someone used "signal chain" to refer to, say, the internal workings of one device, but let's say you have a mic preamp connected to a recorder of some type, which then sent its output to a mixer, and then that went out to a stereo recorder. The entire path from the mic plugged into the preamp to the mix-down recorder (IMO) would be referred to as the signal chain. I may be wrong, but this seems to be a common use, and fits with what you are asking. Now, for console buses.

    For the longest time, I also wondered what the Hell you would need auxiliary buses and things for, but we'll get to that in a second. First and foremost, a bus is any audio signal or set of signals being routed to a particular destination. So, the most obvious bus in a mixing console is the stereo main bus, which is basically taking all of the mixed channels and sending them to the stereo output of the console. So, when you are mixing a bunch of channels, and then controlling the master output of the console by the stereo main fader, you are altering the output of the main stereo bus.

    From there you will generally find auxiliary buses that can send the audio from selected channels to a single output, aside from the stereo main. One use of this is if you want to have a seperate mix for different players in a group. The Yamaha MG32, the mixing console I use for recording and live performances, has 4 auxiliary buses that each channel has access to. If you take a look at the picture of the console, you will see 4 knobs in each channel strip (the vertical strip of knobs corresponding to each channel) that represent the amount of signal being sent to each of the 4 auxiliary buses.

    Let me give a quick description of a possible setup using the board for a recording session, and then show a potential use for the 4 auxiliary buses.

    Channel 1: Vocal mic
    Channel 2&3: Guitar amp
    Channel 4: Bass amp
    Channels 5-8: Drumset mics

    At the board:
    Each of the mics is running into some sort of multi-track recorder, which then runs into the sound board, on individual channels, so each channel represents one of the mics listed above. Then, a 4-set headphone preamp is setup with each auxiliary bus's output running to one of the headphone preamp channels. Then there are 4 sets of headphones plugged into the headphone amp.

    If everyone is listening to the recording session while they are playing, each person probably wants to hear different things (either a musician prefers to be able to hear his or her own instrument more or less than all the others). So, you could go through each channel on the board, and set channels 1-4 to a lower output volume than 5-8 using the Aux 1 volume knob. When the signal runs out the Aux Bus 1 jack into the headphone amp, the drummer can hear the drumset louder than all the other instruments. Then do this for the other musicians on the other Auxiliary buses, but mix their respective instruments higher, and send those mixes to the appropriate sets of headphones. Now, each musician can hear themselves louder than the other instruments, so they can follow what they are doing.

    A live example might use them for the following... Say you have the same setup as above, accept now the board's main output runs to a PA system, and you have a full mix of all the instruments going to the PA system. Most singers like to have stage monitors in front of them so they can hear themselves while onstage, without having to wear an earpiece or headphones. You could go to the lead vocal channel (in this example), channel 1, and crank up the Auxiliary Bus 1 volume, and then send the Aux Bus 1 output to a powered monitor sitting in front of the singer. This way, the mix going to his or her personal monitor is just the vocal line, not the entire house mix... this makes it much easier to hear what is being sung, and all the unwanted band sounds are filtered out (since the singer can hear all that anyway!).

    A last example I can think of involves the auxiliary bus returns. While each channel has auxiliary bus outputs, there are also auxiliary inputs to run back into the board, mainly for the purpose of attaching processors, effects units, etc. Let's say you have a nice digital reverb unit that you would like to apply to the vocal line, and to no other channels, so you can't just run the final output mix through the effects unit, and then into the power amp / PA system. You could run the output from auxiliary bus 1 to the effects unit, and then run the output from the effects unit back into one of the auxiliary bus returns. Then, whatever channels you would like to apply reverb to, you simply turn up the knob for auxiliary bus 1 to the desired amount. Then, you turn up the Auxiliary Bus 1 Return knob to add that returned reverb unit's signal to the final mix. This gives you the flexibility to add a particular effect to whatever channels you please, and gives you the ability to leave channels clean that you don't want processed. It also allows you the freedome to hook up whatever external processors you want, instead of being limited to any on-board effects (if there are any).

    I know this was ridiculously long, but hey - I'm bored at work. If it was confusing or you have any questions, keep on posting!
  3. hueseph

    hueseph Well-Known Member

    Oct 31, 2005
    Vancouver, BC, Canada
    Good description of buses.

    I call it a signal path but that's just me. In my mind the most important signal path you need to consider is the one in your mixer. There are the obvious things that you see and plug into but in the mixer the signal path has a large affect on how your recording turns out.

    First: the mic to your preamp. This is obvious. From your preamp whether it be in your mixer or outboard the first thing it meets it the trim pot for that channel. Generally all signal goes to it's destination pre fader. Why does it matter? If you send the signal pre fader, nothing you do to change the signal after the fader will effect the recorded signal. Therefore, any level adjustment needs to be made at the source, preamp or at the trim pot. So if you record a signal where the trim pot is not properly set and try to compensate with the fader, you will be very dissappointed and will have to redo the track.

    Eq is usually post fader unless there is an option to switch it to pre fader. Why? This ensures that the signal going to disc or tape maintains it's fidelity, If you need to make changes to the track after it's recorded, you can do it. If it is pre fader You're stuck with any eq you apply. Effects and inserts are usually post fader as well.

    This is where it comes in handy to learn what those schematic diagrams are all about. You don't have to be able to decipher them entirely but if you can get a gyst of where the signal goes ones it enters the mixer it'll help you get your job done a lot easier.

    Please anyone feel free to correct me. :lol:

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