Bass and room modes test with music CD


If you are frustrated by playing with a Rat Shack meter and test tones (frequency tones, warbles, pink noise, 1/3 octaves etc.) and never quite sure what you should "fix" or what you should just live with (no room is ever perfect)....then this may be the CD for you.

Rebecca Pidgeon, The Raven, Chesky CD.

What follows is taken from Bob Katz excellent book on Audio Mastering. The track "Spanish Harlem" on this CD, in the key of G, uses the classic 1, 4, 5 progression. Here are the frequencies of the fundamental notes of the bass.

49......62......73
............65..........82.......98
....................73..........93..........110

Check it out.

In the absence of a test CD with real music I spent hours playing with test tones/Rat Shack meter/PEQ... and initially I went overboard with a PEQ trying to fix everytyhing as near flat as I could in the LF. In the end, I did not like the sound when it was equalized flat and went back to a minimal PEQ approach with a few minor adjustments on the worst offending peaks but never crushing the sound into conformance. (trial and error process playing many CD's)

Yesterday I received the above CD and played Spanish Harlem track. WOW - it works. You can easily HEAR immediately how balanced it is. (Real notes on a real instrument seem far easier to balance in your head than test tones...I can't explain why but that was my experience...perhaps it's the harmonics)

I realized that this CD could have saved me an enormous amount of time.....it lets you judge how the room modal bumps, incorrect sub settings and/or placements are actually affecting a real instrument.

Unlike the Rat Shack meter this allows you to gauge the amount of tweaking necessary. For me, a 3 db bump over a 6 Hz interval is much better simply left alone rather than mercilessly PEQ for flat reponse; but a 10 db bump is an audible intrusive problem clearly affecting the balance. In any case, the CD lets one precisely judge the relative effects on music.)

IMHO, PEQ adjustment to get a flat response, whilst easy to do, is far from ideal because it adjusts the primary signal in order to get the combined primary and room modal signal down (the room modal response is the real culprit and, although not always practical, room treatment/design is by far the ideal solution)

...just thought I would share this. Any comments from anyone who faced this issue or perhaps has found another solution or another good test with music CD?
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Showing 5 responses by eldartford

Like you I found the RS meter game to be a lot of frustrating work, and never really effective. My solution is a Behringer DEQ2496 automatic equalizer with spectrum display. (Three of them actually, to take care of five channels). I equalize for the total sound at the middle of my room, but if you wanted to do just the primary signal you could put the mic up close to the speaker. However, if your speakers are any good this would result in very little equalization. Room effects are really what it's all about.
Warnerwh...You forgot to mention how easy it is to get a non-flat response with the DEQ2496 if that's you want. You simply adjust the "target" curve (what the auto eq aims for) until it looks like what you want. Then do auto eq.
Newbee...Frankly, I think that a 100 watt amp with 86dB speakers pumping out a SPL of 85 dB is pushing limits even without any eq boost. However, room eq, insofar as you keep the SPL within the capability of your speakers and power amp, will definitely make an amazing improvement to any ststem.

The spectrum analysis display might help you to minimize that dip in your system's response by different speaker placement, room treatment, etc. Also, if the dip is 12 dB, a lesser boost, like 6 dB will help a lot.

The key feature of the Behringer DEQ2496 is that it is so darned inexpensive ($300 and change including mic and mic cable) that most audiophiles can afford to try it. And try it you must. Don't listen to speculation about how it sounds based only on its price or its digital implementation. Your ears will convince you.
Shadorne,,,The DEQ2496 includes a "cut only" function, "Feedback Destroyer" (ten filters) has a bandwidth range of 1/10 to 1/60 octave. The Parametric Equalizer function (ten filters) has filter bandwidth range of 1/10 to 10 octaves. The graphic equalizer function is 1/3 octave...31 bands. The spectrum analyser display is 1/6 octave...61 bands.
Shadorne...It does not include the mic, because professional users may already have a mic, and may also use several DEQ2496, and they don't all need their own mic. Buy the Behringer mic, and don't forget you will need a balanced line mic cable.

If you want more info you can download the complete owner's manual from the website. It looks complicated, but with a little hands-on experience it ain't that bad.

You seem to have a lot of preconceived ideas about limiting the use of the unit. I bet that once you get one to play around with these ideas will change!

FWIW, I bought mine at www.samedaymusic.com.

Have fun.