Thanks for the replies.
Sorry, but there aren't technical write-ups for DSP plugins.
Our DSPs are 32-bit, use high-quality filtering mechanisms, and are often tuned by ear.
Is there nothing more you can add about the characteristics of the subwoofer filter?
I'm not at all concerned about quality - J River is very good at delivering a good product. Besides, if a system needs the subwoofer EQ, it's already compromised. I'm looking to use the effect for my outdoor speakers which are small and need some help at the low end.
I'd really like to understand at least the basic nature of the transfer function. I'm just looking for a basic low end boost, preferably shelved, that only works below a chosen frequency. Just what a bass tone control does, only much lower in frequency than what's typical on many receivers.
So if the subwoofer effect does this, then I'm done. If not, I need to look further.
It almost sounds like I'm getting into proprietary waters here and I really hope that's not the case....