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Receiver output

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  • Receiver output

    Does the receiver always send a certain amount of power to the speakers, or does it depend on the actual signal coming through the receiver?

    ie: If I leave my receiver on say 60% volume, with the input (my laptop) on 100% volume, does it use more power than if I were to leave it on 60% volume, but lower the volume on the laptop?
    -I live in Madison, WI (what a boring sig right? :))

  • #2
    in short-- it varies based upon the actual signal coming into the receiver....

    But if you want a more detailed answer, then let's take this a few pieces at a time... first,

    output power = (gain) x (input signal)

    where gain is your receiver's volume setting. if your input signal is from a laptop then the equation will have a few more terms:

    output power = (gain) x (input signal gain) x (input signal)

    where input signal is the ultimate upstream signal (MP3 waveform) and input signal gain would be the product of the windows operating system's "volume level" as well as the MP3 player software's "volume level" (e.g. windows media player). So for instance, your receiver could be on "half" (0.5), your windows OS could be on "one-quarter" (0.25) and your MP3 player could be on "three-quarters" (.75). That would lead to an output power of:

    output power = (recevier volume) x (windows OS volume) x (MP3 software volume) x (MP3 waveform)
    output power = (0.5) x (0.75) x (0.25) x (MP3 audio waveform)
    output power = (0.09375) x (MP3 audio waveform)

    but note that your receiver can only go up so far.. so if your Windows and MP3 player software stayed where they were, your receiver could only go to unity gain (1.0) or maybe just a smidge higher (1.1 or so) ... in such a case the max you would get (again, assuming your windows OS and MP3 player software volume controls were left at .25 and .75) woud be:

    output power,max = (1.0) x (.25) x (.75) x (audio signal)
    output power,max = (0.1875) x (audio signal)

    if you needed it louder, you'd need to increase the output volume of the MP3 player and/or Windows OS.

    The next important thing to note is that unfortunately there is not one "absolutely universal standard" for getting music from one device to another. There are a few assumed standards for many consumer electronic devices, but that's beyond the scope of this reply. Suffice it to say that it is possible for "too hot" a signal to be put into your receiver. That will cause distortion/clipping/evilthings to occur. How to get "the closest to without breaching" the receiver's maximum input signal is also a bit out of the scope of this reply, but can be discussed if necessary. The short answer to that question is "read the manuals" (of the reciever and your computer sound card)... :) (hint: pay attention to the specifications of voltage levels for the audio inputs and outputs of each device.)

    So, what we're left with STILL reduces down to the product of an "overal" gain (the product of all volume controls / gain settings including the receiver and all upstream devices), and the level of the audio waveform itself:

    output power = (overall gain) x (audio signal)

    resulting in the same answer above--- a varying audio signal will result in a variable amount of output power, whether the variation comes from the audio signal itself (a quiet whisper versus a loud explosion) or an up-stream gain control (windows "volume control").

    hope that helps,
    (The first to sport a signature on TCAforum..)
    "Be kind, for everyone you meet is carrying a great burden." - Philo of Alexandria
    "Love God and be nice to people." - Brooks Everett of CBC
    d&k's webpage


    • #3
      Wow, that was quite the post Dane! Very informational. "thumbsup:


      • #4
        Oh wow, it did help no doubt. Thanks a mil!
        -I live in Madison, WI (what a boring sig right? :))


        • #5
          Your standard sources such as a CD/DVD player will have a fixed output.

          In the receiver the volume acts as a valve for that incoming signal. If you have the volume turned all the way up it's like opening a faucet all the way.

          Typically a receiver is producing very little power to drive your speakers until it gets really loud.

          Now with an adjustable output device such as your laptop things are a little different. The line out/ headphone jack of a laptop has a volume control built-in. It's needed for headphones but not necessary for the line out.
          Unfortunately, when the volume of the laptop is maxed out it very likely will cause the signal to become distorted due to the headphone amplifying portion of the circuit.

          So it may be better to set your laptop volume at around 60-75% of full volume so as to avoid sending an already distorted signal to your receiver.

          If you prefer to control your overall volume from the laptop then it's just a matter of experimenting with balancing the volume of your laptop with the receiver and figuring out what works best for you.


          • #6
            So how do you go about figuring if/when any particular audio component is distorting the signal?

            I suppose I could just dial back everything 10%, but I still wouldn't know.

            Let's say I did dial back by MP3 player volume and my laptop master volume
            down by 10%. So, I've got (.9 x .9 = .81) approximately 80% of the original encoded signal strength. If I want to get back to reference, I'd have to run my receiver past 0bB, and I'd probably never get there, right? Would I run out of dial, or would the power sections of my receiver run out of "juice"? I guess my question here is "is the power consumption of the amps in my receiver based on signal output, or % amplification?" (Now that I'm thinking about it, is this what the OP is actually trying to get at?)

            So assuming I can't back to reference - let's look at this from a different angle. Say I want 80% of reference (whatever that is), so I turn my calibrated receiver up to 0dB. If my amp can power my speakers, which can play it without distorting, I should have clean audio, right?

            Now, maybe I can determine that my MP3 player and laptop can transmit their signals at 100% without distortion. If I want the same 80% of reference (again, whatever that means technically) I just turn my receiver to that setting. In these last two cases, are the output signals identical?

            That's a lot of rambling, but I think the question about power consumption vs %amplification or output level is the heart of the shortcomings in my understanding. I'll probably sleep on it and come to see it more clearly tomorrow, but I'd like to hear others' thoughts.



            • #7
              I can reply more next week, but the short answer is that the volume control (aka gain setting) has very little to do with listening to something "at reference volume." Reference volume is either 75dB or 85dB, depending on what calibration system you use, at the listening location. There is plenty of documentation online about calibration techniques and I'm sure others could post links to some better methods faster than I could (re)find them.

              Distortion is a worthy consideration, to be sure. Typically speaking setting your MP3 software and your Windows OS both to "100%" is the proper approach. This way the original encoded audio file (mp3, flac, etc) is passed through to the sound card without any processing (to "lower" the volume). You need to also make sure you have all soundcard "effects" disabled.. If you're using a well known name brand soundcard (internal or external), the above approach is just fine.. Then use your AVR for your volume control.

              If you are bent on figuring out what's going on in the signal path between computer and AVR, then get yourself REW (room eq wizard) and you can actually MEASURE the THD+N (total harmonic distortion + noise) in your complete output path. REW will both generate a sweep as well as measure the return signal, so it can calculate those things. THD+N on everything excluding the amp section will likely be at or below 0.005%. Amplifiers are a bit more diffiicult to measure (for reasons beyond the scope of this reply) but a good amp will be at-or-less than about 0.05% THD+N. A stellar amp will be probably less than 0.01%. A tube amp will actually exhibit much more THD+N. I don't recall ranges but I would venture a guess that even a stellar tube amp might still measure 1-5% THD+N. Why tubes "sound better" even though they add more distortion is WAY out of the scope of this thread (and can be highly debated).

              "Typical" listening outputs certainly less than 10wpc (watts per channel).. usually more like 1-6wpc. It's the occasional drum kick or cannon blast that can ever-so-briefly draw upwards of 500W (or much much more). For 85% of enthusiests, I think 85wpc or more is perfectly sufficient unless there are extenuating circumstances such as highly IN-efficient speakers, a VERY large room, a very (acoustically) DEAD room, etc. Most homes are not that way (IMO).

              To your other question-- the power output is based SOLELY on the signal level going to the final power amplification stage. That takes place after going through ALL preprocessing algorithms. Simulated surround sound modes, volume controls, etc. The volume/gain setting is simply one piece of the pre-processing equation. The FINAL audio signal that goes to the power output stage determines the power draw of the system. The final power output stage is typically a FIXED 29dB (most common) or 34dB gain (less common but does exist) amplification stage. You don't really need to know terribly much about the details. A 1dB signal gained by 29dB will be 30dB. a 10dB signal gained by 34dB will be 44dB. Whatever the FINAL output is equates to the power output. A low input signal gained a lot draws the same amount of power as a hot input signal gained very little, so long as the two output signals have the same magnitude.

              I would not worry about your receiver's power draw, unless it's on 8+hrs per day, 7 days per week. Your water heater, washing machine, A/C units, oven, dishwasher, microwave, hairdyers, etc. take MUCH more power than your receiver....

              (The first to sport a signature on TCAforum..)
              "Be kind, for everyone you meet is carrying a great burden." - Philo of Alexandria
              "Love God and be nice to people." - Brooks Everett of CBC
              d&k's webpage