Processing

DRC-FIR software

To equalize my arrays I’ve made use of the free software package DRC-FIR written by Denis Sbragion.

To learn this software I’ve used it experimentally for a period of about half a year, trying to find the boundaries of what I could and what I couldn’t hear. I experimented with the many variables, by looking at what they do and how I perceived those changes. Instead of using it for room correction (which the name implies) I was mostly interested in what it could do for speaker correction, or rather: correcting the first wave front that hits our ears.

Some of that wave front will be direct sound, some of it (mainly the lower notes) will be largely influenced by the room, due to their specific wave lengths. With arrays, we can diminish the effects that the floor and ceiling have on the sound as perceived by the listener. Not really valid for the whole frequency curve with these 3.5″ drivers, but true for the most important part of music: the entire mid-range. At least, that’s what I regard as the most important part of music, as most of what we perceive around us is mid-range sounds. We are less critical of the top and bottom end, as part of our survival instinct. That does not mean to say we should neglect the upper and lower parts, but with a speaker like this specific array, it compromises the top and bottom reproduction somewhat to really shine at mid frequencies.

My use of DRC-FIR has changed somewhat trough the years. While at first I figured it was a tool that could get me awesome results in mere minutes, the more I learned, the more the tweaking of the results started. So these days I still use DRC-FIR, but it isn’t the end of the line, just a start from which I create my desired correction. I use complimenting tools to slowly grow to my end result. I use DRC-FIR to quickly create a basic FIR correction, all minimum phase in nature. After a new round of measurements I move on to tools like rePhase to make further tweaks. Both minimum phase as well as linear phase tweaks to get to my desired end result.

rePhase

In my old ways of doing things I’ve tried all kind of ways to create a filter within DRC-FIR to clean up the output of the speaker as well as take care of room anomalies. Trying to use mixed phase filters (meaning a mixture of minimum phase and linear phase) to get instant results. I’ve found that by correcting the output strictly with minimum phase filters using DRC-FIR, and after that step making a couple of add-on phase tweaks with rePhase, I was able to get cleaner overall end results.

rePhase is a very versatile tool created by Thomas Drugeon. At first it was meant to compensate the phase for known or named crossovers, it has grown over the years to become a tool to be able to manipulate phase by EQ-ing it separately from  magnitude and many more features. the end result is saved in a FIR filter which can be used in a convolver tool for playback. It has numerous output formats and even the windowing used is adjustable.

Care must be taken for these kind of tweaks, it’s quite easy to overdo it or even mess it up totally. To do it well, one needs to learn how to read the room and the speakers, preferably be able to separate the two. Not an easy task and reason why Tools like DRC-FIR and rePhase or even DSP in general often get a bad reputation. Not a deserved reaction if you ask me, probability is high that it was User error that lead to the less than desirable results.

Personally I can recommend both these apps as useful tools once you put  in the time to learn the ropes. Manipulating the audio stream isn’t simple and can degrade the quality quickly if one isn’t careful. But it can also lead you to very satisfying results that are the icing on the cake.