From: Patent Tactics, George Brock-Nannestad
the record you have may be a key. I suspect that there are dB indications
opposite the frequencies you indicate. In themselves they are obviously
worthless for absolute measurements. However, if you were to measure the
modulation by means of the light-bandwidth method (Buchmann-Meyer, promoted
in the US by Benjamin Bauer), then you could relate the dBs to the absolute
recorded velocity, and the total of all the figures would indicate the curve
that the recording was cut with--with the resolution given by the table of
frequencies. This process is not difficult to perform, but you have to take
care with getting the light-source right.
> Hi Kevin,
> As a semi-recovered record collector, there are only a few things
> that I still collect - one of those being test records.
> I have RCA 2346-1 (web back), "Test Record for RCA-NBC Orthacoustic
> Recording" with tone sequences:
> What I don't know, is the date of this test record. It orginates
> from Montreal (ie. RCA Victor Company Limited, Montreal).
> This RCA-NBC tone disc was part of a collection of transcriptions
> dating from 1945 thru 1947. I don't know when web back discs were
> produced, but that may help book-end the possible date range for
> this test record.
> I'll check my servers to see if I have a digitized (FLAT EQ) copy
> of this disc for analysis.
> Eric Jacobs
> The Audio Archive, Inc.
> tel: 408.221.2128
> fax: 408.549.9867
> mailto:[log in to unmask]
> Disc and Tape Audio Transfer Services and Preservation Consulting
> -----Original Message-----
> From: Association for Recorded Sound Discussion List
> [mailto:[log in to unmask]]On Behalf Of Kevin P. Mostyn
> Sent: Tuesday, January 26, 2010 1:47 PM
> To: [log in to unmask]
> Subject: [ARSCLIST] Orthacoustic Curve
> I'm seeking advice from the group as to the correct (or recommended) bass
> turnover frequency for Orthacoustic transcriptions.
> I note that this has also been called Orthocoustic (Audio Cyclopedia by
> Tremaine) and Orthoacoustic (many users.) A U.S. Patent
> ...from 1940 refers to Orthacoustic. Furthermore, I have several 16" NBC
> lacquers from the late 1930s boldly rubber-stamped as Orthacoustic.
> A Google search of available literature, as well as reference books in my
> collection, make various claims as to the turnover frequency. Common
> are 700 Hz and 500 Hz, as well as several ranging from 400 to 1000 Hz.
> is no consistent recommendation that I can find in the manuals for various
> preamplifiers which have variable playback equalizations.
> When I studied filters in the 1960s, it was common to refer to the
> frequency of an equalization curve as that point at which the curve
> from a reference point by 3 dB. A common reference point for audio filters
> was 1 kHz.
> The curve displayed in the above referenced patent is insufficiently
> detailed to estimate the 3 dB point. It makes reference to 500 Hz, but, in
> my opinion, that is not the 3 dB point as shown.
> The "Orthocoustic" curve in the Audio Cyclopedia by Tremaine (1st edition,
> 1959) on page 431, figure 13.99, shows a 3 dB point at about 700 Hz,
> referenced to 1 kHz. The curve in the Radiotron Designer's Handbook (4th
> edition, 1953) page 730, figure 17.15, is insufficiently detailed for my
> weak eyes to discern, but it may be 3 dB at 500 Hz.
> I should say that I believe that the correct equalization curve is that
> which yields accurate sound reproduction on a calibrated loudspeaker
> but that is of course highly subjective.
> Thanks for any help!
> --Kevin Mostyn