Analog error-correcting codes (Analog ECCs), introduced by Roth [1], address errors in vector-matrix multiplication arising from analog noise and sparse outliers in in-memory computing. A fundamental open problem concerns the lower bound on the single-error correction threshold
Γ2(C) for real
[n,k] linear codes with fixed redundancy
r=n−k≥2. Li et al. [2] recently established that for redundancy
r=2, every real
[n,n−2] linear code
C satisfies
Γ2(C)≥csc2(2nπ), resolving an open problem in [1], and showed that, for every fixed
r≥2, there exists a class of
[n,k] linear code
C over
R such that
Γ2(C)≤O(n1+r−11). This paper proves the matching converse in [2]. For every
[n,k] linear code
C⊆Rn with fixed redundancy $2\leq r