Hi, guys,
 
I have to clean 40 audio lectures (speech only) of about 2 hours - 170MB each, and they're in MP3 - 128kbit/s.  My questions are:
 
1- Is it better to convert the files to mono before cleaning?
2- I know that Sonar has a lot of resources to do the cleaning but I was wondering if Melodyne (stand alone) could do the task easier, even for big files (I didn't work with Melodyne yet and I purchased the editor edition), or you recommend another plugin inside Sonar? I really wanted something very straight forward for not loosing too much time in this project, the files are too big and there's some pops and cracks...
3- After the cleaning, would you recommend any effects or is it better to let them dry?
4- Since I'm gonna have to fit all the files in one 4.7GB DVD, what do you think is the minimum bitrate I can use to do the task without harming so much the audio?
 
Thanks a lot for any help!

I would not recommend any kind of conversion unless necessary.  I also don't see a reason to use melodyne for this sort of thing unless you want to alter the timing or pitch of the lecturers voice.  Is there a lot of background noise? If so, was ambient sound desired or did you want it as clean as possible?  I would start with EQ or filter depending on level of ambient noise you want in the background.  A little rolloff of the low end might help and maybe a-3 db notch between 200-400 hz.  You may have to sweep to find the right spot. For a lecture, I would not bother with any effects like reverb.  Maybe a little compression or e leveler. If the recording sounds a little sterile, one of the nomad eqs may warm it up some.

You could probably get away with encoding at a lower bitrate than 128 for just raw speech.  We notice differences a lot more in musical applications than ordinary speech.  I would render test files out at 96 and as low as 64 and give them a listen.

Not sure if Sonar can analyse a noise sample and them remove it. I know it can be done in Audacity. You select a section of the noise as a sample, then it removes that noise from the entire track. Problem is that sometimes it changes the sound of what you do want to keep.

@leebut
Sonar X3 does not have that built in, but  if you have X2, it came with R-mix which is capable of decent noise reduction. An FYI on using noise reduction plugins like the ones found in Audacity, Audition, and Sound Forge:
 
 1. Make sure you have enough of the actual noise you want to remove. Whenever I record sound on location, I record a good minute of the environment so I have a good variety of the type of noises that may be in a room.
 
2. Also, you will get less damaging results on applying noise reduction if you use modest settings.  Applying Auditions noise reduction twice at 50% will give much better results than once at 100% no matter how good the noise print is.
 
3. The more distinct the noise is, the better your results.  A beeping alarm clock is much easier to remove than background chatter.
 
4. If the noise is of the white noise variety that is hard to separate from what you are trying to record, skip the noise reductin plugin altogether.  You will just get a very tinny sounding voice.  Exceptions to that are things like forensic work where the goal is simply to extract something intelligible.
 
When I find myself in a situation where the white noise or chatter is too much to remove using noise reduction, I usually use a combo of filters and gates.  Be careful with noise gate beccause it can sound odd if you have background noise during speech and dead silence otherwise.  A way to fill in the silence but at a level that is controllable in ratio to your main speaker is to make a loop of the ambient recording.  on another track in your project.  It will make the sound between the gated parts sound more natural
 
 
 
 

dubdisciple,
 
when I finish the cleaning process, I'll have to make the 40 files fit in the medium, the size they all have now surpass the size of a 4.7GB DVD, so that I have no choice, I'll have to compress in a lower bitrate...
 
I thought that Melodyne could separate the voice from noises or artifacts in the blobs. In fact, the files have only some pops & crackles here and there and, as they were recorded in a big theater with 300 people, we can hear ambient noise also.  I'd like to have them as clear as possible.  I'll try your Eq. suggestions.
 
And what about converting to mono, do you think it makes any difference in working with these files?
 
Thank you very much!

Do you have melodyne editor?  The version that comes with Sonar will not process polyphonic material.  I doubt even Editor can do the task you speak of. but let us know if that works. Converting to mono will reduce the file size.  I doubt you will run into phase issues.

leebut,
 
I've already tried the noise reduction in Audacity but I didn't like the results, probably I didn't tweak it the right way...  I'm gonna put together all the advices and see what I can learn to get this job done.
 
Thank you very much for the reply.

dubdisciple,
 
Yes, I have the editor, I benefitted from the promotion.
One of my concerns in converting the files to mono was related to phase issues but you kind of allay me.
 
Thanks again!

Not sure if this is a big job or the type of work that will be re-occuring.  With that said one of my associiates is a film producer and He has used Izotopes RX3 to clean his film tracks. This is dedicated to that kind of task and appears extremely intuitive to use. Tasks are organized preset style that are customizable and the tools can be used in any DAW as a plug in. IHTH....