Date:         Fri, 1 Feb 2008 19:42:06 -0500
Reply-To:     Association for Recorded Sound Discussion List
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Sender:       Association for Recorded Sound Discussion List
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From:         "Richard L. Hess" <[log in to unmask]>
Subject:      Re: Digital File Specs and StoryCorps
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At 07:18 PM 2008-02-01, Tom Fine wrote:

>What are the bias frequencies of cassettes? Did it vary by 
>manufacturer or was there a standard? Did it vary by tape type? 
>Sorry if these are ignorant questions. Richard will know where I'm 
>going here ...
>
>Does any cassette playback system stand a chance of reproducing bias 
>so Jamie Haworth's Plangent Process can be used on it?

I think the likelihood of a standard deck (such as a Dragon) 
reproducing the bias from its output jacks is highly unlikely.

I posted the following to this list on 2006-07-04; 2008-02-01 
revisions are marked *

In the early days, apparently wire recorders used bias as low as 
30-40 kc, but Jay McKnight recalled in the pre-Ampex days, 60 kHz was common.
The Ampex Standard was 100 kc up to the MR-70.
With the MR-70, Ampex switched to 150 kHz bias frequency (and adopted 
the Hz) [Larry Miller, ex Ampex]

Other later machines used different bias and erase frequencies.

Ampex AG-440 (A) stayed with 150 kHz [manual]
Ampex ATR-100  144 kHz erase, 432 kHz bias  (1:3)  [manual]

MCI JH-24 Multitrack 210 kHz bias, 105 kHz erase  [manual via Brian Roth]

Otari MTR-10/12 II Bias 250 kHz (erase not spec'd) [manual]
Otari MTR-90 (original) 246 kHz bias, 123 kHz erase [manual via Brian Roth]

Sony APR-5000, APR-24  100 kHz erase, 400 kHz bias (1:4) [manual]

Studer A80 80 kHz erase, 240 kHz bias (1:3) [Jay McKnight]
    *This applies to the Studer A80 VU apparently
*Studer A80 RC 150 kHz [manual]
Studer A810 & A807 (and I think A820 2CH) 153.6 kHz  [manual]
    *A820 2CH confirmed at 153.6 kHz
ReVox A77  120 kHz [manual]
*ReVox B67  150 kHz [manual]
*ReVox B77  150 kHz [manual]
*ReVox PR99  150 kHz [manual]

Here is a quick sampling of published bias frequencies for two 
top-of-the line cassette recorders, a better-than-average portable, 
and an early compact portable.

Nakamichi Dragon (perhaps the finest machine ever made for overall 
audio quality) 105kHz (Service manual dated 1985 (scan) 1990 (Xerox))
Studer A710 (a high-end cassette recorder, without the auto-azimuth 
that makes the Dragon superior) 150kHz (no date, scan on Studer ftp site)
Sony TC-D5M (a workhorse, good quality stereo portable) 85 kHz (Svc 
Manual dated 1980)
Sony TC-55 (an early compact -- jacket pocket -- mono portable) 41kHz 
(as low as I've ever seen) (Svc Manual dated 1972)



Richard L. Hess                   email: [log in to unmask]
Aurora, Ontario, Canada       (905) 713 6733     1-877-TAPE-FIX
Detailed contact information: http://www.richardhess.com/tape/contact.htm
Quality tape transfers -- even from hard-to-play tapes.