What Does Bass Look Like?
To understand you need to get to know the waterfall charts linked to "bassy scenes" in the FAQs section. But to really understand what the 3D waterfalls are showing, you may first require a brief overview of the tools used to measure them. A real time analyzer (RTA) is an instrument used to convert signal from the time domain (amplitude vs. time), to the frequency domain (amplitude vs. frequency). If you're familiar with an ordinary oscilloscope you know what a time domain display looks like. A frequency domain display is known as a spectrum. Unless you are measuring a single tone, an oscilloscope provides little in the way of frequency information. A spectrum analyzer clearly reveals this information however. An audio spectrum analyzer then, by definition, is limited to processing signals in the audio band.
I use Spectra Plus ™. It's a powerful software based RTA program that will provide accurate results with today’s modern PCs. You can DL a free 30-day demo of Spectra Plus ™ by clicking here.
Those of you familiar with my Spectra Plus ™ derived “Bassy Scenes” posted in various internet forums probably know how to read a basic frequency vs. amplitude chart. The horizontal axis shows the frequency in Hertz (Hz). The vertical axis shows the amplitude.
The advantage of using this type of measuring “view” is that a single JPG image can support several "bassy scenes" at once. The disadvantage to using this frequency vs. amplitude display is it cannot support any "time" considerations. This is precisely where the 3D “waterfall display shines. The 3D waterfall is a PERSPECTIVE VIEW remember the old Zaxxon arcade game?) of the spectral data --- over time! That's right, not only does the 3D waterfall record frequency and amplitude.... it also records this data over a specific time “slice”. This it the best view for understanding the dynamics of a particular "bassy scene".
Now that you have a basic understanding of what a RTA is, and what the term 3D waterfall means...let's get more specific regarding the 3D charts on the SVS website.
How did I measure them?
I connected the subwoofer pre-out of my processor directly to the soundcard input on my laptop computer. I set all the speakers to SMALL--- 80hz crossover. Subwoofer to YES,80hz crossover. I use the same volume setting for all the 3D charts...roughly 23dB under reference. At times I vary the 3D chart "range" (how wide an amplitude range it can show)...but only when I feel doing so would enhance the meaning of the chart.
How should I interpret the 3D waterfalls?
Above is a 3D waterfall of the LFE "sweep" on DVD Spectacular (one of the first test DVDs). Note the sweep starts at the TOP of the 3D chart. This is very important to remember. The 3D waterfalls measure time...and display it from top to bottom. Think of the 3D chart as a conveyer belt....and it's a belt that is moving AWAY from your point of view (down here where the frequency scale is). So...as the LFE sweep starts at 20hz (22hz actually--a glitch in DVD spectacular) the 3D display measures the signal...and the whole time the belt is moving "up"...so as the sweep continues...the belt is moving up farther and farther. I stopped the measuring of the LFE sweep, right before the beginning of it was about to "roll over" the edge of the display. As I have it setup now...I can measure about 8-10 seconds of a particular “bassy scene”....so I couldn't fit the whole LFE sweep from DVD spectacular on a single 3D waterfall.
Another VERY important point when reading these 3D waterfalls is that you need to be aware of the *angle* of the chart flow. Look at the left ”edge” of the chart. It doesn't extend straight *up* --- it extends at a slight angle...about 15 degrees or so. So, when reading these charts...and trying to reference the frequency figures at the bottom of each graph to the data on the chart.... you must remember, the frequency boundaries move up—at a slight angle. Look at the LFE sweep once more...note that even though it starts at about 22hz (remember---it's a DVD spectacular glitch)...it appears to start around 30-35hz upon casual glance.
The next 3D chart I would look at is the BLADE footsteps JPG.
Here's what you can pick out from that chart once you know what to look for...
- 3 distinct onscreen steps. Remember, starting from top to bottom...you should be able to make out 3 separate “booms”...each rolling off rapidly before the next hits.
- Note that the first step (toward the top of the chart) is the loudest. How can you tell that? Easy, look closely at the first step...and you can see the chart actually “anvils”. That is...the chart plateaus suddenly, indicating the signal was so high (loud) that it went off the scale I was using for this scene.
- Even though the first step was the loudest, it's max. energy seems to be 30hz and above. The 3rd step appears to extend a bit lower though...perhaps peaking around 27hz.
- If you look at the upper-most part of the chart...you can see a little noise all the way down to 10hz...this is the growling/snarling that occurs right before BLADE takes his steps.
If you got this far...try looking over some of the other 3D waterfalls. Play the track on your HT as you view the JPG ..and I think you'll begin to correlate the data you're seeing to the bass you're hearing. Or should be hearing. Remember, many, if not most commercial subs just don’t produce much of the bass you see graphically represented on these charts. Another reason to go SVS.
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