As far as I know, fixing low quality samples isn't easy. An 8khz sample doesn't actually have any of the higher frequencies, so you can't exactly recover them.
I looked for such a program a while back because I bought a sound CD with lots of poor quality samples, but I never found anything better than what I could do manually with sound forge, and I wasn't exactly doing a great job on them.
The best you can probably do is convert the sample to 44khz and 16 bit, and then try to use the equalizer on it. You'll be trying to get back some of the higher frequency sounds so the sample doesn't sound like it has so much bass. I don't think you'll ever get anything approaching a clean sounding sample with good frequency range though. At least, not with my level of sound editing expertise or less. I don't know what an expert sound designer could do with such a sound, but I suspect they wouldn't even bother with it and would just buy a better sound or make their own.
Btw, there was a sound cleaning plugin I had for sounf forge at one time. It was intended for removing noise in a sample. The idea was you would select a blank section of your recorded sound, which had static, and it would remove those frequencies from the main recording, thus canceling out noise. But this only really worked if you had a sample which had blank space so you could build the noise profile. And if I remember correctly it didn't really do anything for low bitrate sample "noise".
I looked for such a program a while back because I bought a sound CD with lots of poor quality samples, but I never found anything better than what I could do manually with sound forge, and I wasn't exactly doing a great job on them.
The best you can probably do is convert the sample to 44khz and 16 bit, and then try to use the equalizer on it. You'll be trying to get back some of the higher frequency sounds so the sample doesn't sound like it has so much bass. I don't think you'll ever get anything approaching a clean sounding sample with good frequency range though. At least, not with my level of sound editing expertise or less. I don't know what an expert sound designer could do with such a sound, but I suspect they wouldn't even bother with it and would just buy a better sound or make their own.
Btw, there was a sound cleaning plugin I had for sounf forge at one time. It was intended for removing noise in a sample. The idea was you would select a blank section of your recorded sound, which had static, and it would remove those frequencies from the main recording, thus canceling out noise. But this only really worked if you had a sample which had blank space so you could build the noise profile. And if I remember correctly it didn't really do anything for low bitrate sample "noise".