Found this RCA Orthacoustic patent filed in 1940 and granted
Correct me if I'm wrong, but doesn't this look like the
Columbia Curve (1590, 318, 100 usec TC; 100, 500, 1590 Hz TO)?
See page 3, item 6 in the above patent document describing the
Seems a little surprising.
Still looking for better references, but this is the best
on-line reference I've found so far.
The Audio Archive, Inc.
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Disc and Tape Audio Transfer Services and Preservation Consulting
From: Association for Recorded Sound Discussion List
[mailto:[log in to unmask]]On Behalf Of Doug Pomeroy
Sent: Thursday, January 28, 2010 10:17 AM
To: [log in to unmask]
Subject: Re: [ARSCLIST] Orthacoustic Curve
Hi Eric and Kevin and Jim Long,
It would be nice to know, once and for all, where Tremaine got the
curve he shows in the Audio Cyclopedia.
Powell's graph shows the-3 dB point of the Orthacoustic/NBC recording
curve as being at about 400 Hz.
The NAB/Orthacoustic playback curve is shown as being +3 at about 500
Hz. Nothing to get excited about,
unless Tremaine got it wrong, and the -3 dB point on the recording
curve should actually at 700 Hz.
Powell's reference is B F Fredendal, from a 1946 Journal, which
cannot be accessed online (I tried):
Fredendall, B. F.
Lateral Disk Recording, Part 1, Broadcast Eng. J., Eng., 8, 13-15
(February, 1947). New developments in pickups;
13, 4-5, 12 (May, 1946). Fundamental principles of present-day
recording. Constant-amplitude and constant-velocity recording
Lateral Disk Recording, Part 2, Broadcast Eng. J., 13, 4-6, 9 (June,
1946). Discussion of sound energy distribution and equalization in
disk recording. The use of the optical pattern in determining the
frequency characteristic of a cutting head.
Audio Restoration & Mastering Services
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> Date: Tue, 26 Jan 2010 14:59:16 -0800
> From: Eric Jacobs <[log in to unmask]>
> Subject: Re: Orthacoustic Curve
> 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 claims
> are 700 Hz and 500 Hz, as well as several ranging from 400 to 1000
> Hz. There
> is no consistent recommendation that I can find in the manuals for
> 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
> 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
> 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
> 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
> which yields accurate sound reproduction on a calibrated
> loudspeaker system,
> but that is of course highly subjective.
> Thanks for any help!
> --Kevin Mostyn
"The only reason for time is so that everything doesn't happen at once."