Untitled Document

Reverberation Impulse Comparison

Frequency Response and Dynamic Range

The principle of convolution offers astounding potential in the area of reverb impulses (RI) previously unattainable with existing reverb technology. Most (if not all) RI renderings of "high end" digital reverb widely available on the internet barely scratch the surface of what is attainable using the power and sophistication true 24 bit convolution can deliver. When using these "freeware" RI's, you are basically using yesterday's 16 bit technology on today's 24 bit system. It is not surprising that these "hardware simulations" do not have the neutrality/clarity or maximum richness of impulses that can be explicitly designed using convolution. Numerical Sound's impulses are the only impulses that have been optimized for true, full 24 bit performance which the following graphs will illustrate.

Six reverb impulses were analyzed and plotted for both frequency and dynamic range. Results are provided in the following three graphic representations:

1. The first graph shows the decay characteristics in decibels of the reverb impulse. (Data is from the left channel). The red line in each graph is the decay rate a realistic acoustic enclosure should follow (down to the noise floor -144db for 24 bits).

2. The second graph illustrates the full frequency response of the reverb impulse. (Note: The frequency range of primary importance is below 1000Hz).

3. The third graphic zooms in on the high frequency response (from 1khz to 20khz). Reverb impulses, by their very nature, should have a jagged frequency response with a multitude of peaks and valleys, however the overall trend line (depicting an average of all these small variations) should be flat.

Given the state of today's technology, there is simply no excuse for a "non-flat" frequency response in a reverb impulse. It makes more sense for a producer to use an EQ plugin (or FFT filter impulse) to alter the sound of the wet signal and have it change dynamically with the musical nature of the mix than resort to various high frequency enhancers or multi-band dynamics processors in order to fix the overall sound.

An acoustic reverb impulse should decay at a constant even rate. When one looks at the first graph for each impulse the line should descend straight down to the noise floor. Impulses should look like the Numerical Sound impulse (#1).

The noise floor and/or smallest signal level in decibels (y axis vertical) versus the number of bits in the sound file (x axis horizontal)