If M4A is lossy and AIFF is lossless (e.g. MP3 → WAV), the AIFF file is no better than the M4A — you can't recover information that's already been thrown away. If M4A is lossless and AIFF is lossy, expect the AIFF codec to recompress; at 192 kbps this is transparent for most content.
By default yes (48 kHz M4A → 48 kHz AIFF). If you need to downsample for compatibility (e.g. 96 kHz → 44.1 kHz for CD burning) the advanced sample-rate option does this with high-quality resampling.
Same-codec re-mux: 10-30 seconds. Re-encode to a different codec: typically 10-20% of source duration, so a 1-hour M4A → AIFF finishes in 6-12 minutes.
Чаро файли AIFF баландтар / хомӯштар аз манбаи M4A аст?
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Агар шумо параметри нормализатсияро фаъол накунед, дигаргунии худкори баландӣ рух намедиҳад. Агар шумо тағйирёбии сатҳро бубинед, плеери аудиоии шумо ё китобхонаи мултимедиявии шумо метавонад ReplayGain ё нормализатсияи ҳар як роҳчаро барои бозикунӣ истифода барад - на мо.