I have tried a lot of the offerings.

The best restorations results I have had is to clean the machine very thourough between each song, waiting for the transport to dry and buff.

Then I align the machine properly for the tape in bias , eq (tape eq 70 or 120 microseconds) and azumuth and usually do a dolby off transfer to hard drive noise and all.

This is the time to go from your hard drive to CDR.

Now you can (after cleaning for each song and analysing) take the CD through analog filters. Parametric eq cut above 8K in steps and peaks and make the content as pure as possible. I roll off below 45hZ pretty steep on cassettes if their is no LF in the program. Noise knows all freqencies so look at the LF cut.

Then after I get the settings I like for each song, I go to hard drive out of the A/D converter to Dig in of computer and cut it to a peak of -10 dB at 16/44.1K.

Then I use very small amounts of computer based software (eq mainly) to restore it one more level and burn the new CDR.

It works effectively.

Dynamics can throw a plug in off balance for different levels.

Try Waves restoration kit. They hav a demo version that will run as a demo for 15 days.
With very old tape transfers, I generally use some HPFs and LPFs to limit bandwidht. Maybe a LPF at 40Hz to eliminate recorder´s self noise and tape hiss with a HPH around 6.5khz. Of course if it is more recent material , there is no need for such a severe filtering.
A BIll mentioned, pick up a good tape player, with access to azymuth controller. :p

I've gotten some remarkable results using the WAVES stuff .

It is extremely important to not overdo it despite the miracle-like impression you'll often get from this technology. I usually only treat beginnings, endings and very soft passages and I've found each of these requires its own sample and settings. It's very rare to just run something through without losing a lot of the musicality and magic of the recording. A LOT of major label reissues have been ruined this way.

Like every other step of production you need to pay close attention to not losing what's right by dwelling on what's wrong. It takes quite a bit of time to do this kind of work properly because it is very hard to keep from getting too close and losing the music.

I have had good results using CEDAR noise reduction.

Used VERY sparingly, Sonic No-Noise might do well also.

In any case, 3 to 4 slight passes will work better than one drastic pass. Be conservative using the settings. Especially on Sonic. Sometimes a combination of devices works better than one type alone.

Usually a combination of EQ and Cedar DeNoise work for me. I love the Cedar stuff but Don's right, several gentle passes is definitely much more pleasing to the ear than one big spank…