This is what i have been using ever since i have been using computers.
Illustrate dBpowerAMP Music Converter R13.2 Reference Edition
dBpoweramp Music Converter™ is 'the standard' tool for audio conversions, with over 20 million users:
Huge range of audio codecs supported: mp3, mp4, m4a (AAC, iTunes & iPod), Windows Media Audio (wma), Ogg Vorbis and FLAC
Preservation of ID Tags and Album Artwork, correct mapping of ID Tags between tag types (where possible),
Multi-CPU encoding support, Easy folder & drive selection with Batch Converter,DSP effect support (ReplayGain, Volume Normalize, including DirectX and VST effects), Pro-orientated codecs: BWF Wave, Dalet, Windows Explorer integration: audio info tips & columns,mp2 It is safe to say, no other audio program converts more multi-format audio files than dBpoweramp, we have spent 8 years perfecting format-compatibility and conversion stability.
FLAC codec included as standard, is default codec for CD Ripper
FLAC codec - internal update to allow 'Front Cover Art' as default
DSP Effects updated to R4
CD Ripper: MetaDataGD3 Symphony - extended classical fields
CD Ripper: naming sections max length increased from 1000 to 10000 chars
CD Ripper: metadata review - red miss-matches shown in bold (for color blind)
mp3 Lame updated to 3.98.2
mp3 Lame added 'Forced Stereo' option on advanced
GetPopupInfo enhanced so can no longer 100% CPU if audio file is corrupted
dBpoweramp Configuration Program Versions redesigned (dAP + Sveta removed, Asset Added)