ValhallaRoom was named for its ability to get realistic room sounds. From this perspective, a concert hall is nothing more than a really big room. The physics and reverberant characteristics of concert halls have been studied extensively in the last century, starting with the work of Wallace Sabine (the acoustic consultant for the design of Boston Symphony Hall) and continuing with the work of Leo Beranek, Yoichi Ando, Manfred Schroeder, and many other acoustic researchers.
Concert halls that are highly ranked by classical music listeners tend to have the following characteristics:
- A mid-frequency decay time of 1.6 to 1.8 seconds for music from the “Classical” period (1750 to 1820), and around 1.9 to 2.1 seconds for music from the “Romantic” period.
- An initial time-delay gap at or below 25 msec. This is the time between the direct sound and the first reflection, and produces a sense of “intimacy” for shorter settings. This is why the “shoebox” shaped halls tend to be preferred by conductors and audiences – the initial lateral reflections start rather quickly, due to the relatively short distance that sound has to travel from the orchestra to the side walls to the listeners.
- “Warmth,” in that the bass tones are strong. This translates to a low-frequency decay time that is somewhat longer than the mid-frequency decay time.
- Spaciousness, in that the sound seems to come from a space wider than the instrument making the sound. This tends to be tied into phase differences in the signals hitting the left and right ears (which is often referred to as the IACC, interaural cross-correlation).
- Envelopment, in that the reverberation appears to come from all directions, rather than from limited directions. In practice, this means that an ideal hall will mix the reflections together rather quickly, and won’t have any strong discrete echos from any one location, or a part of the hall where the reverb hangs around too long (as can happen in cathedrals with high naves).
Starting with the above criteria, we can dial in a realistic concert hall preset in ValhallaRoom. A few general principles:
- Set DECAY to 1.6 to 2.1, depending on the type of music that will be played in the space.
- Set HIGH CUT to a fairly low frequency, between 4500 Hz and 7000 Hz, to simulate the air absorption in the space.
- PREDELAY should be set to match the initial time delay gap of the hall being modeled, with 25 to 35 milliseconds being a more “realistic” setting, and shorter settings useful in generating intimacy.
- The Early Size parameter should be between 20 and 50 msec, with Early Send turned up full and Early Diffusion at max, in order to product a diffuse onset of reverberation.
- The Late Size should be set greater than 0.5. The largest settings of Late Size may produce audible reflections, depending on the mode used, so tune this by ear.
- The Late High Xover should be set low enough to cause a bit of rolloff in the decay (around 2 to 4 KHz), and the Late High Mult should be set to values significantly lower than 1.0X.
- Late Cross should be set higher than 0.0, in order to simulate the envelopment of real halls. Late Cross values less than 1.0 will help retain the spatialization of stereo inputs, so this should be tweaked according to taste – start at 0.5 and work your way up or down.
- The Early Mod Depth should be set to 0 for realism – higher values result in an unnatural panning of the early decay. The Late Mod Depth can be set higher than 0, and a little bit of modulation helps enhance the realism, but keep the Late Mod Rate in the 0.25-1.0 Hz range to avoid obvious pitch changes.
As a quick example, here’s a preset based on the measurements of Boston’s Symphony Hall, as described in Leo Beranek’s “Concert Halls and Opera Houses”:
[sourcecode language=”xml”]<ValhallaRoom pluginVersion="1.0.5" presetName="SymphonyHall" mix="0.333000004" predelay="0.0671999976" decay="0.0180180185" HighCut="0.408053696" earlyLateMix="0.699999988" lateSize="0.74000001" lateCross="0.730000019" lateModRate="0.111111112" lateModDepth="0.720000029" RTBassMultiply="0.400000006" RTXover="0.0313131325" RTHighMultiply="0.533333361" RTHighXover="0.216778517" earlySize="0.0394394398" earlyCross="0.0299999993" earlyModRate="0.0909090936" earlyModDepth="0" earlySend="1" diffusion="1" type="0"/>[/sourcecode]
A quick tweak of the above, with a change of the Reverb Mode from Large Room to Large Chamber (just to shake things up), and we have a model of Vienna’s Grosser Musikvereinssaal:
[sourcecode language=”xml”]<ValhallaRoom pluginVersion="1.0.5" presetName="GrosserMusikvereinssaal" mix="0.425000012" predelay="0.0240000002" decay="0.0194194186" HighCut="0.371140927" earlyLateMix="1" lateSize="1" lateCross="0.709999979" lateModRate="0.103030302" lateModDepth="0.720000029" RTBassMultiply="0.433333337" RTXover="0.0909090936" RTHighMultiply="0.5" RTHighXover="0.258389264" earlySize="0.0441441424" earlyCross="0.0299999993" earlyModRate="0.0909090936" earlyModDepth="0" earlySend="1" diffusion="1" type="0.333333343"/>[/sourcecode]
It is worth noting that I haven’t been to either of the above halls in person, so take the above presets as a rough starting point for creating your own concert hall presets.