Originally Posted by jim19611961
When i speak of controlling early high reflections, a full band ETC is not adequate. You must look at different frequency regions via ETC slicing to see what different ranges are doing. It is quite common for example for the full range ETC to meet our goals (first 20ms < -20db) , but have the 1K or 500hz 1 octave slices fail miserably to meet this same goal. What we want here is early reflection attenuation across as broad a range as possible.
Jim, we recently spent some time receiving guidance on how to generate and interpret the Spectrogram, with good results. I perceive this to be another opportunity to enhance the collective knowledge of thread participants. I acknowledge you as being an expert on managing reflections, and an expert at using ETC as one of your tools. Can you help us understand in more detail how to leverage the filtered impulse response to identify and correct room reflections?
Here are several snapshots of the same impulse response measurement (full range, 500Hz, 1000Hz, and 4000Hz, at both full octave and 1/3 octave):
Here are several questions that would help interpreting the graphs:
1. For the 500Hz graphs, the same filter at 1/1 octave and 1/3 octave seems to show different reflections. The 1/1 seems to show reflections at 12, 22, and 27ms, while the 1/3 is showing only a reflection at 18ms. Please explain what we are seeing.
2. Looking at 500Hz, 1000Hz, and 4000Hz, I seem to be seeing different reflections. I recall from previous discussions that reflections that are present at higher frequencies, but missing at lower frequencies, are caused by smaller surfaces. Is that correct, or is it the other way around?
3. Using the filtered graphs, can you point out something that these graphs reveal that we might miss if we were only looking at the full-range graph?
4. Can any of these measurements help in locating multiple-surface reflections, which seem to be especially difficult to identify and eliminate?
Understanding the impulse response measurement has become very important, IMO.