Aparokshaanubhuti is a prakarana of Bhagavan Adi Samkara. It takes a suitable saadhaka to the self realization.
Bhagavtpaada's description of mounam, maunam or silence:
यस्माद्वाचो निवर्तन्ते अप्राप्य मनसा सह | यन्मौनं योगिभिर्गम्यं तद्भवेत्सर्वदा बुधः ||१०७|| वाचो यस्यान्निवर्तन्ते तद्वक्तुं केन शक्यते | प्रपञ्चो यदि वक्तव्यः सोऽपि शब्दविवर्जितः ||१०८|| इति वा तद्भवेन्मौनं सतां सहज संज्ञितम् | गिरा मौनं तु बालानां प्रयुक्तं ब्रह्मवादिभिः ||१०९||-- http://sanskritdocuments.org/all_sa/aparokshaanbhuuti_sa.html
107. The wise should always be one with that silence wherefrom words together with the mind turn back without reaching it, but which is attainable by the Yogins.
108-109. Who can describe That (i.e., Brahman) whence words turn away ? (So silence is inevitable while describing Brahman). Or if the phenomenal world were to be described, even that is beyond words. This, to give an alternate definition, may also be termed silence known among the sages as congenital. The observance of silence by restraining speech, on the other hand, is ordained by the teachers of Brahman for the ignorant.