There are Vedic mantras and Tantric mantras... Vedic procedures and Tantric procedures. Tantric means quickly, directly without long procedures and texts.
Vedic mantras are Vedic texts used in Vedic procedures of worship. Tantric bija mantra is short, condensed esence of vedic mantras... like... you can worship Vishnu through Purusha sukta from Rig Ved and related procedure or you can worship Vishnu through Tantric procedure with single bija mantra. Result will be the same. In these days there are no pure Vedic or Tantric procedures. They are mixed. But Vedic mantra has meaning as Tantric mantra. If somebody says different then he did not go deeply in investigation of Vedic and Tantric texts and procedures. Every single sound in Universe has meaning. There are no meaningles sounds.
