I've found the groove width as measured at the top (disc surface) to
be on the order of 55 microns on average. The groove bottom is rounded
and can be poorly formed. The ideal playback stylus is 0.77 mil or
19.4 micron conical.
The problem with an LP stylus (0.7 mil) is that most will drag along
the bottom of the groove and not get good wall contact, resulting in
In lieu of the ideal stylus, a 1.0 mil TE (truncated elliptical) will
work well (1 mil = 25.4 micron) and is easily obtainable from Expert
Stylus. It rides a bit higher along the groove wall but doesn't hit
the groove bottom. It doesn't ride so high as to start picking up
cross talk from the adjacent groove.
The absolute largest stylus that will track the groove on a flexi-disc
is 2.1 mil - but this will pick up a fair amount of surface noise and
cross talk from the adjacent groove, and will be especially susceptible
to skipping and repeating - so this is NOT recommended.
I've noticed that the distance between adjacent grooves on these
flexi-discs are on the order of 20-25 microns on average, but can
literally touch on loud passages. So cross talk is a real issue.
I have some photomicrographs taken through my microscope that
demonstrate what such cross talk looks like at 150x magnification.
The worst problem I encounter with these discs is when they've been
stored with a paper clip attached to them (either to group the discs,
or to clip some identifying information to the disc). This leaves
a crease in the outer edge which is nearly untrackable at any VTF
and with any amount of tape. In this case, your only choice is
low temperature flattening and annealing (specialized equipment).
As others have pointed out, fully supporting the disc is critical
to minimize noise. Because these discs are so thin, wherever they
are unsupported (ie. warp or non-flat support surface), there will
be a signficant increase in noise. I use a 100% graphite platter
that is smooth and flat to 0.0001 inch, and the graphite provides
good damping characteristics in order to minimize noise. A record
clamp keeps the disc both flat and from slipping.
With the right stylus, a flat disc, proper support surface, and
a properly aligned cartridge, it's possible to obtain a very
high S/N. The final result can actually sound "tape like" in its
broadband noise character.
It is important to obtain a high S/N on many of these recordings
because the speaker may move closer and farther from the microphone,
or the recording level may be low, or there may be ambient background
sounds... all of which may make comprehension of the recording difficult.
If you just want to hear what is on the disc, using a microgroove
stylus (NOT an LP stylus) will work reasonably well. A 1.0 mil
or 1.2 mil truncated elliptical stylus will work better. If you're
doing a LOT of these and can justify a made-to-order stylus, get
yourself a 0.8 mil TE or 0.8 mil conical.
Another consideration is that many of these recorders were not
terribly precise when it comes to speed. Fortunately, the electronics
were not fantastic either, and if you're lucky you'll find some
hum together with the signal. You can then use the hum to get
the speed right. But if your S/N is not terribly good, the hum
may get lost in the noise. So yet another argument for maximizing
This type of transfer work is fairly straight-forward with the right
equipment and tools, and some knowledge of the media characteristics
as described above.
The Audio Archive
mailto:[log in to unmask]
From: Association for Recorded Sound Discussion List
[mailto:[log in to unmask]]On Behalf Of Adrian Cosentini
Sent: Tuesday, July 17, 2007 5:09 PM
To: [log in to unmask]
Subject: Re: [ARSCLIST] Playing a "flexi disc"
These are nothing like EvaTone Sound Sheets (or discs). It's a whole
other headache. Yeah and good luck tracking even with a micro groove
styli. I collected a bunch of styli just to deal with these mess'. Oh
yeah and there's the tracking and the pitch angle to deal with and
then.... it goes on and on. Not for the faint of heart if you want to get
the max S/N and dynamic range. But that's a whole other story.
On Tue, 17 Jul 2007 19:30:24 -0400 Tom Fine <[log in to unmask]>
> If this disk is somewhat akin to the later EvaTone Soundsheet, I've
> had very good luck playing those
> by placing them on top of a non-valued LP record. Another trick I've
> had success with is taping down
> the squared corners with regular old Scotch tape, so the disk lays
> flatter. This is not necessary
> all the time. I have dozens of EvaTone Soundsheets and have been
> able to transfer all of them with
> usually very good results.
> -- Tom Fine
> ----- Original Message -----
> From: "Wasserman, Robert A - WHS"
> <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Tuesday, July 17, 2007 4:15 PM
> Subject: Re: [ARSCLIST] Playing a "flexi disc"
> A suggestion, most modern turntables are not flat enough for these
> discs, place a piece of board or cardboard similar in size and shape
> the disc with a hole in it to create a flat surface. You might need
> small piece of tape on the back (if one sided) or near the edge if
> cardboard surface is too slippery.
> Robert Wasserman
> [log in to unmask]
> Sound Archives Proj. Asst./Lead Tech.
> Wisconsin Historical Society
> Dear Barbara Need,
> If the disc is translucent green vinyl, it may be a Soundscriber
> disc. These were 33.3 rpm microgroove, so you should try to play it
> as if it were an LP. Pray that it hasn't warped; if it has, you may
> need to send it to someone with excellent equipment and much
> Sincerely, Richard
> At 02:59 PM 7/17/2007, you wrote:
> >I have been asked to get a digital transfer from what I believe to
> >be a "Flexi disc" (thin green plastic /vinyl disc with a square
> >hole). The only complication is that, as far as I can tell, these
> >were LPs and, therefore, no earlier than 1948. The date on the
> >however, is '43. We have an osmium stylus (which we use for
> >78s) and a diamond stylus (which we use for LPs). What stylus
> >should I use for playback? (And if you have recommendations for
> >adding to my stylus supply, I would welcome that as well, though I
> >may not be able to do anything about it just yet.)
> >Barbara Need