Embedded Reverberation-Time Measurement for Classroom and Office Acoustics: Block-Length and Precision Limits on ISO 3382 Compliance

Reverberation time (T60) decides whether a classroom or open-plan office is usable for speech, yet certified analysers cost thousands of dollars, so most rooms are never measured. This paper models a complete exponential-sine-sweep (ESS) reverberation-time measurement chain on a TMS320C6748-class embedded processor and asks whether arithmetic limits (overlap-add block length, word length, filter realisation) can push the result outside tolerance. A Python simulation shows that overlap-add block length does not bias the result, because block-wise convolution is algebraically exact; the variable that matters is the length of impulse response the device retains. Fixed-point arithmetic with block-floating-point scaling stays within 0.3 % of a double-precision reference from 12 bits upward, and single-precision floating point is adequate unconditionally. The octave-band filter bank adds under about 1.5 % error for T60 ≥ 0.3 s. The expanded uncertainty is at most 1.9 % for all rooms tested. All results come from synthetic rooms and a flop-count cost model; validation on public databases and live rooms remains to be done.