Space Designer IR Sample rate in Final Cut Pro
The Space Designer effect’s Sample Rate slider determines the sample rate of an impulse response.
Orig: Space Designer uses the current project sample rate. When loading an impulse response, Space Designer automatically converts the sample rate of the impulse response to match the current project sample rate, if necessary. For example, this allows you to load a 44.1 kHz impulse response into a project running at 96 kHz, and vice versa.
/2, /4, /8: These settings are half-divisions of the preceding value—one-half, one-quarter, one-eighth. For example:
If the project sample rate is 96 kHz, the options are 48 kHz, 24 kHz, and 12 kHz.
If the project sample rate is 44.1 kHz, the options are 22.05 kHz, 11.025 kHz, and 5512.5 Hz.
Changing the sample rate upward increases—or changing it downward decreases—the frequency response (and length) of the impulse response, and to a degree the overall sound quality of the reverb. Upward sample rate changes are of benefit only if the original IR sample actually contains higher frequencies. When you are reducing the sample rate, use your ears to decide if the sonic quality meets your needs.
Note: Natural room surfaces—except concrete and tiles—tend to have minimal reflections in the higher frequency ranges, making the half-rate and full-rate IRs sound almost identical.
When you select half the sample rate, the impulse response becomes twice as long. The highest frequency that can be reverberated is halved. This results in a behavior that is much like doubling every dimension of a virtual room—multiplying a room’s volume by eight.
Another benefit of reducing the sample rate is that processing requirements drop significantly, making half–sample rate settings useful for large, open spaces.
Turning on Preserve Length preserves the length of the impulse response when the sample rate is changed. Manipulating these two parameters as you see fit can lead to interesting results.
The lower sample rates can also be used for interesting tempo, pitch, and retro-digital sounding effects.
If you are using Space Designer in a project that has a higher sample rate than the impulse response, you may also want to reduce the impulse response sample rate. Make sure Preserve Length is turned on. This cuts CPU power consumption without compromising reverb quality. There is no loss in reverb quality, because the impulse response does not benefit from the higher project sample rate.
You can make similar adjustments using Space Designer in Synthesized IR mode. Most typical reverb sounds don’t feature an excessive amount of high-frequency content. If you were running at 96 kHz, for example, you would need to make use of some deep lowpass filtering to obtain the mellow frequency response characteristics of many reverb sounds. A better approach would be to first reduce the high frequencies by 1/2 or even 1/4 using the Sample Rate slider, and then apply the lowpass filter. This conserves a considerable amount of CPU power.