In operating my IC-7300 one thing that I noticed and has been noted by others as well is a rather noticeable low end roll off below 200hz on both receive and transmit. This results in rather flat sounding receive and transmit. A good way to experience this is set the tone controls at flat for both AM and SSB. Next, tune in a strong local AM station and note the bass response when listening in AM then switch to SSB and note the difference. Also due to this behaviour the bass tone control does not have anywhere near as much effect on both AM receive and transmit compared to SSB. The IC-7300 has a provision for providing a 12khz IF output from the USB cable. The manual explains this was intended for DRM reception. However, it can also be demodulated by using an SDR program and this provides a 12khz wide output of the receive section. When I did this one thing that I noticed is that the 200hz roll off did not exist when using this 12khz IF output. I then tried feeding audio back into the USB port such as one would do when operating digital modes. To my surprise I found that the 200hz roll off was not present on AM transmit as well. I spent some time looking at the service manual to see if I could gain any clues and the only thing that I was able to find was that the accessory port and USB cable are fed by a different pin on the D/A as compared to the microphone and speaker/headphone out. However, this doesn't tell me much as the bass roll off does not exist in SSB mode on either receive or transmit. Another thing I noticed is that Icom uses the same DSP libraries across several radios. I'm quite confused as to why Icom would implement a roll off that is only present on AM on both receive and transmit and yet the IF out is not subject to this. If anything, you hear about restricted frequency response more often on SSB than AM. I'm also curious as to where this IF out is derived from in the circuit. What is peculiar, though, is how if you change the mode or filter width on the radio when using the 12khz IF out you can hear the change on the demodulated audio but changing the receive EQ on the radio has no effect. I have been using SDRuno for demodulating the IF out and listening to the resulting audio. While all of this may sound like a minor detail the difference in receive quality when deriving the audio from the IF out versus the speaker/headphone out is quite dramatic. It turns the receive quality from something that can be quite tiring to a much more enjoyable and listenable experience. Any ideas or information regarding this would be greatly appreciated.