Just to make some things clear if you're going to be doing this in dBpoweramp via trial/ogg vorbis codec (separate download on their website):
After starting the batch converter "ogg vorbis" should be set to resample to 24Khz (frequency), set to Quality (VBR) and drag the slider furthest to the right (variable bit rate is VARIABLE it will not effect quality and is efficient so long as you give it the wiggle room.), leave rest of variables "[as source]". Make sure to click "add" at the bottom right of the batch manager, Add DSP Effect > ID Tag Processing, click "Deletions" tab and select "all tags" to the right. (ID Tags have been known to cause unusual delay with radios in the FO3 engine, I don't know if this bug is present in FNV.) [Wave should be set to uncompressed and only frequency should be changed to 24Khz, repeat same step regarding ID Tags.]
Mind the format, if you are converting wav, set the filter to wave, for ogg vorbis click ogg and deselect the others. They need to be the same format, so you should be prompted for an override. The converter will remember the settings for each codec.
Don't bother converting any mp3s, the ones you need to convert are wav and ogg format. One thing to remember is bethesda softworks archives have audio files packaged with other assets, don't be fooled by file names. (If in doubt check the BSA in BSA Browser.) I recommend converting all ogg/wav files. This can be a time consuming process, but IMO worth it.
Use your favorite BSA extractor, personally I use FOMM's BSA Explorer standalone (a fork on the skyrim nexus.)
One last note, at the time of writing there are no tools capable of repackaging audio assets into Bethesda Software Archives, so you'll be loading these as loose files to your game. (Mod Organizer or NMM is excellent for managing loose files, alternatively you can backup the default contents of your music/sound folder for a painless restoration. (Another method is to use SFV ninja tool to generate a checksum file for comparison prior to dropping the loose files in.)
Contraindications: Interestingly, FNV has some (very, very few) dialog/sounds in 32KHz, left to speculation perhaps a mistake, or perhaps 32KHz would work, I'm not up to testing to find out.
Big thanks to RoyBatty for the sample rate info/advice and inspiring me to find a free method to convert the audio on a mass scale in early-mid 2015. [img]https://www.taleoftwowastelands.com/sites/all/modules/drupalchat/smileys/very_emotional_emoticons-png/png-32x32/high_five.gif[/img]