I am trying to fix some audio problems about sound directly recorded via a preamp on a canon 5d, a sort of auto gain and limiter was inserted so all material raise 0 dbfs, and there are also a lot of noise problems, like hisses on long part of material, many dialogues in car scenes with many problems (noise spectrum cover voices). My very basic and immediate approach to all ths was to cut with eq at 5 kz, and put an highpass filter at 50hz, noticed that the use on a noice reducer like wns and an wave ultra maximizer can helps to let dialogue come out and to give uniform dynamic of all dialogues. What would you do ? consider that budget is low and times are very reduce.
I'm sorry to tell you that this is probably lost. And also I think it's a waist of time (sorry again). There is no tool or way to make something good from bad. If you start filtering, repairing spectrum, you don't make it good, you only make it a little less bad. It needs do be proper recorded or replaced.
Recording in cars: If the engine is on and the interior of the car is full of noise, it's important to give actors lav-mics. (Renting a lavalier here in switzerland costs me $20.-) If it's possible to do the take without the engine on, you can start playing in post with clean vocal tracks (a miracle: a lot of the foleys where also here if the engine's off) an adding the engine sound from the library or record it later. This is sound editing and makes fun and the time should be used for that instead of trying to repair hopeless audiofiles. But it needs do be planned and considered BEFORE shooting.
"budget is low and times are very reduce"
Its the old triangle of diminishing returns: Fast, Good or Cheap. Pick two Sounds like what you're working on is cheap, fast so its not going to be good
What is the final destination of the project? Where will it be seen/heard?
"cut with eq at 5 kz, and put an highpass filter at 50hz"
You should be able to get away with the low cut but I wouldn't put a global 5k cut - like all dialogue you will need to deal with it on a shot by shot basis.... But maybe doing a sort of the material so all your 'hiss' takes are on a couple of dedicated tracks, rumbly on another set etc so you can fine tune semi-global EQ...
Of course all the usual dialogue editing techniques should be used, time permitting - alt takes, clean fill, wild lines, ADR etc..
BUT ALSO: do you plan to ever work for these people again? If so, this is your opportunity to show them WHY they must record sound properly, and hook them up with a production sound person for their next project. Sadly I see people with $20k DSLR rigs, with a Beachtek adaptor, a cheap mic & no one monitoring it, who think they are capturing 'good' audio - their gear budget for sound isn't even as much as their cheapest lens