Master Frequency Registry

The Master Frequency Registry is the Tower's principal index of sustained vibrational signatures, recorded not in cycles per second but in adjusted hertz (AdHz), the unit obtained by subtracting the ambient hum of the stairwells from any measurement taken within earshot of them. The Registry is maintained on Floor 23 by the Bureau of Persistent Oscillation under the standing authority of Concordance 88, and is not to be confused with the Aggregate Echo Map, which indexes the same frequencies but sorts them by echo return rather than by origin. The distinction matters chiefly to people who have filed the wrong form.

Entries are arranged by frequency band, each band assigned to a Registry Band Warden who certifies that the signature it contains has been heard at least twice by two separate clerks. Bands above 300 AdHz are certified by three clerks, one of whom must not have been present for the first two hearings.

History

The Registry was established in the winter following the Collapse of the Eighth Gallery, when it was discovered that the sounds which had caused the collapse had been noted in four separate ledgers under four different designations. Concordance 41 had already provided for the indexing of frequencies in principle; it had neglected to say by whom. The Bureau of Persistent Oscillation was accordingly founded by Concordance 88, which assigned it the Registry and, in the same clause, the maintenance of the tuning forks used to calibrate it — an association the Bureau has petitioned to sever nine times.

The first Recension of the Registry, compiled over eleven years, listed 340 signatures. The Second Recension listed 1,102, of which 288 proved on review to be the same signature heard in different weather. The Third Recension, current, lists 2,140 signatures and an appendix of 61 that are known to exist but have declined to be measured. The appendix is maintained at the insistence of the Office of Reluctant Phenomena.

Procedure and the Case of Clerk Ambrose

Measurement is by comparison with the calibrated forks, heard alternately with the subject signature until the two are indistinguishable to the measuring clerk. The procedure is repeated on a different floor, since frequencies are known to alter with altitude, and a signature that survives all three hearings is entered in the Registry in ink; one that does not is entered in pencil and reviewed at the quarterly reconciliation.

In the winter of the year the East Scriptorium was refloored, a clerk named Ambrose of the Second Fork recorded a signature of 47 AdHz in the East Scriptorium, heard it again on Floor 23, and failed to hear it a third time anywhere in the Tower. He entered it in pencil, as the procedure requires. He then spent, by his own account, "fourteen years and a considerable portion of my hearing" pursuing it, and in his final year submitted a memorandum arguing that a signature which cannot be re-heard is not absent but has merely declined to repeat itself, and should be promoted rather than erased. The memorandum was received, stamped, and filed under Correspondence, Declined. Ambrose's signature remains in the Registry at 47 AdHz in pencil, with a marginal note in his hand: still there. The note has been annotated by three successive Wardens and none has removed it.

The Divergence of the Aggregate Echo Map

The Registry and the Aggregate Echo Map have disagreed since the Map's third revision over whether a signature should be indexed by where it begins or by where it returns. The Bureau of Persistent Oscillation holds that origin is prior and that the Map's method produces a frequency index sorted by architecture, which it describes in its standing preamble as "a geography wearing a number's clothes." The Cartographic Echo Office, which maintains the Map, holds that a signature which does not return was never a frequency to begin with. Both cite Concordance 88, which supports both positions in adjacent clauses, and Concordance 112, which supports neither.

"Where a signature is heard at origin and not at return, the origin shall be entered in the Registry and the return in the Map, and neither office shall amend the other's entry."

— Concordance 112, Annex 6, clause (c)

In practice the two offices have not spoken since the Reconciliation of the Twin Annexes, and correspondence between them is routed through the Master-Archivist, who returns it unopened with a note explaining which of the two registries it should have been sent to.

Relationship to Other Holdings

The Registry draws its band divisions from the Master Sequence Registry and its plotting conventions from the Master Registry of Proven Connections; a frequency entered here without a corresponding line in the latter is treated as unproven and marked accordingly. It is frequently consulted alongside High-Frequency Oscillatory (50–200 AdHz), whose band it overlaps but does not duplicate, and its discrepant entries are reconciled each quarter against the Master Index of Resolved Contradictions. Clerks are reminded that the Registry is not an inventory of sounds heard in the Tower, which is a different document kept by a different office, and that the two have not agreed on a total since the Fourth Recension was abandoned unfinished.

Access

The Registry is consultable on Floor 23 during the hours the forks are not in use. Visitors are asked to remove their boots at the threshold, as the floor was laid for listening and has not been replaced. Signatures in the appendix may be requested by name, but the Office of Reluctant Phenomena notes that requesting one has, on eleven recorded occasions, produced a hearing, and that a hearing produced by request is not admissible as evidence of anything.