Which processors to use ?
I would recommend a FIR processor or software because it is easier and more precise for correction EQ (and it can also correct phase). You can either use a hardware FIR processor or process with software.
Here are some hardware possiblities I have worked with (prices are approximate and indicated without VAT) :
- QSC QSYS, max 16384 taps per channel (with max total about 4×8192 for model Core110F), completely configurable, multichannel ie 8in/16out , very very complete features but a bit costly (about 4000€ for the smaller Core110F)
- Trinnov, max (about) 4096 taps per channel (with total depending on stereo or multichannel model), high end product but you can only use Trinnov’s own software to mesure and EQ, not cheap (starts at 4000€ for stereo models). The new Nova line is cheaper but I did not have time to test it yet.
- MiniDSP OpenDRC, max 6144 taps per channel (with total of 2×6144), cheap and stable, only available with digital I/O, less than 300€
- MiniDSP 2x4HD or Flex, max 2042 taps and min 6 taps per channel (the total of 4096 for all channels gives 2042+2042+6+6). Both are cheap. Because those processor work at 96kHz, the FIR correction file of 2042 taps at 96kHz is equivalent to 1021 taps at 48kHz.
- Xilica Solaro QR1 or FR1, max 4096 taps per channel (with max total of 6×4096 but FIR cannot be loaded into presets so cannot be changed on the fly, contrary to QSys), completely configurable (not far from QSYS) with choice of different I/O boards and nice possibilities to remote with Ipad or Android tablets, (increased !) prices start at about 2000€ for QR1 (8 slots for I/O boards) and 3000€ for FR1 (16 slots) without I/O boards (analog boards are reasonably priced, strange that AES is highly priced). Note that those processor can ran at 96kHz but the FIR length is still 4096 taps so less efficient in the lows…
- t.racks FIR DSP408 : max 2048 taps per channel limited to a total of 4096 taps for all channels together but quite cheap, under 600€
- Eversolo DMP-A8 is a streamer that also provides FIR filtering with 2048 taps per channel for about 2000€
- You also may have a look here at another list of FIR processors.
On the sofware side, you may use a convolution engine such as Brutefir, intregrated into a player or a streamer. Equaliser APO or Camila DSP are also nice solutions. Software are very cheap or even free, they need a computer (small ones such as a Raspberry Pi are ok) but need more configuration, not so easy for everyone.
Because hardware processors may be limited on processing power (FIR taps), they also have IIR parametric filters so you can adjust the LF EQ if you have not enough taps for a precise correction in very low frequencies. In France, QSYS, Xilica and Trinnov can be bought at Company 44.1 (with optional configuration and on-site setup)