Rob’s Tech School Part 4 – Audio (Part 2)

Posted by on February 5, 2013 at 9:30 pm
The beauty of sound

The beauty of sound

Yesterday I started a 2 part lesson on audio and what all those goofy terms that get thrown at you by all of the equipment manufacturers mean, as part of a bigger series on technical stuff, where I talk about frame rates, video resolutions, audio goodness, etc. I talked about frequency response and dynamic range and told you that today I would be talking about dB (decibels) and signal to noise ratio.

Both of these things are pretty important as well because they are constantly used when giving performance stats on audio hardware.

So what do they mean?

First we’ll talk about the decibel, which is notated as dB. This can take several forms because decibels are used to measure a number of things including voltage (dBv, dBm, etc…) and sound pressure levels, or what we commonly call “volume” (dB). In this case, we’re obviously talking about sound pressure so we’re just using dB…And no we won’t be talking about micropascals or particle displacement because this is an article about terms and definitions, not acoustical engineering.

Simply put, a decibel is a unit of measurement. Specifically, it is one tenth of a Bel, but a bel is almost never used because decibels kick ass. Decibels are logarithmic, meaning it is measured in intervals.

Confused yet?

Ok, all you really need to know is that, in this case, more dB = louder. ZERO dB = silence and a Saturn rocket firing is around 190 dB. At anything over 130 dB, you would experience discomfort and start to suffer hearing loss.

Decibels are important because that’s how we measure things like signal to noise ratio, which is very important when you’re selecting audio components because this is a measurement of the ratio of signal (sound) to noise (crap) which will be produced by the gear you’re looking at. Signal to noise ratio will often be expressed in a single number like >90 dB which means that you get more than 90 decibels of sound for ever single decibel of crap. The rule here is “more is better”. (unlike THD or “Total Harmonic Distortion, which is expressed as a percentage…in that case, LOWER is better)

And here’s what we’ve learned in the last 2 lessons. We’ve learned that frequency response tells us what sounds a device can make and that we can hear from 20-20,000 hz. We’ve learned that “perfect sound” is expressed as 20-20,000 hz at a tolerance of 0.0 dB and that dB is a logarithmic system of measurement (base 10, if you were curious). And finally, we’ve learned that signal to noise ratio tells us how much good sound we get, versus how much crap we get.

Now we’re ready to go buy some HEADPHONES!

Speaking of headphones, tomorrow I’ll be reviewing the Xtatic Pro 5.1 headphones from Sharkoon. You’ll want to read that.

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