Audio information for noob

[excellsior]

I'm getting excited looking at all these awesome setups but I have no clue what all the specs and parts are.

I just found out what DAC was and wondered why does someone need to convert to analog?

Besides that, I have no clue what all the specifications mean. Can someone school me all there is to know. Thanks

IE what's this all mean?
Onkyo TX-SR605
Peak Total Power Output: 630 W
THD at Rated RMS Power (Unbridged): 0.08 %
Watts Per Channel (Rear): 90 W/channel
Watts Center: 90 W
Watts Per Channel (Main): 90 W/channel

 

[SpaceHonkey]

If your ears could hear 0's and 1's then you would not need a DAC.

 

[wildfire99]

Speakers (and our ears) are analog devices, thus they require analog signals to drive them. At some point, you have to translate the digital information into an analog waveform. The better the DAC is, the better of a job it will do in simulating an analog signal from the digital signal.

For the Onkyo, the total power output is the theoretical maximum power the device will use when pushed to the limit. It's usually a completely meaningless value, something of a mix between e-peen and marketing speak. In the Onkyo's case, they're simply taking the per-channel wattage (90) and multiplying by 7. Another common marketing trick is PMPO, or peak momentary power output, which is basically what the unit would provide for a fraction of a second before it blows up, should you ever attempt to turn it all the way up.

Since audio is a dynamic thing, you usually won't need more than a fraction of that power at any one time, however for very loud parts of the audio (such as an explosion), you need more of it to drive the speakers to play louder. The more wattage the receiver can push, the louder (again theoretically) you can play the speakers.

The wattage per channel is given since some models don't apply the same power to all channels, usually because of electrical current limitations. In that case, you might see more power being available to the speakers that do the most work, the front mains and center.

Now, what does the available power (as expressed in wattage) mean to you? Generally, it's maximum volume. You take the sensitivity of your speakers (expressed as a decibel per watt figure), and that's the volume you'd get if you fed them with one watt. Each doubling of acoustical power (3dB) requires twice as much electrical power. Thus, if you have speakers that are 87 dB/watt, you would get 87dB worth of sound (measured as SPL) out of them with one watt. To get to 90dB, you need 2 watts. To get to 93dB, you need 4 watts. And so on. Because of this, the difference between say, 90watts and 200 watts is very little (3dB change from 90 watts to 180 watts). The average person requires around 10dB of actual gain to perceive a doubling of loudness, even though 3dB is an actual doubling of SPL.

THD is a rating of how much the electronics are damaging the signal as it passes through them. This should be a very low figure, always under one-tenth of a percent, and preferably lower. Anything over 1 percent is considered to be kind of sloppy these days (IMO). The more you push the circuit, the more distortion is introduced, so the rating here is saying that at worst, you're getting 0.08% THD.