Hi Gang,
Regarding "Slow Reel-to-reels" , vari--speed does NOT due the rest. Heads
with particularly narrow gaps should be used to read snail-pace tapes.
Having that extra resource permits
better extraction of highs than does pedal to the metal eq. adjustments.
JRF has made superb specials for me for my repro-only AG 440.
Best Regards,
Art (Shiffy) Shifrin
On Sun, Apr 15, 2012 at 12:00 AM, ARSCLIST automatic digest system <
[log in to unmask]> wrote:
> There are 4 messages totalling 241 lines in this issue.
>
> Topics of the day:
>
> 1. Slow Reel-to-reels
> 2. Recording_78rpm_records/analog vs digital eq (3)
>
> ----------------------------------------------------------------------
>
> Date: Sat, 14 Apr 2012 10:11:02 +0200
> From: Shai Drori <[log in to unmask]>
> Subject: Re: Slow Reel-to-reels
>
> Stock machine goes down to 3.75. Varispeed does the rest. At these
> speeds I use my ears for eq more than the set standards. The key is the
> gap of the head.
> Shai
>
> בתאריך 04/13/12 10:14 PM, ציטוט Stephen Bolech:
> > Shai, did you have it modified to play at those speeds, or do they have
> that as an option?
> >
> >
> > On Apr 13, 2012, at 2:59 PM, Shai Drori wrote:
> >
> >> I use the Ampex atr-100
> >> Shai Drori
> >>
> >>
> >> בתאריך 04/13/12 8:57 PM, ציטוט Stephen Bolech:
> >>> Hi everyone, I'm hoping some of you could give me recommendations for
> good options to play back 1 7/8 ips and even the occasional 15/16 tapes.
> We have a large oral history collection, and though the majority are at
> 3.75 ips, there are some at these slower speeds. What are you guys using
> for these speeds, and what do you recommend?
> >>>
> >>> Thank you,
> >>> Stephen Bolech
> >>>
> >> --
> >> בברכה,
> >> שי דרורי
> >> מומחה לשימור והמרה של אודיו וידאו וסרטים 8-35 ממ.
>
> --
> בברכה,
> שי דרורי
> מומחה לשימור והמרה של אודיו וידאו וסרטים 8-35 ממ.
>
> ------------------------------
>
> Date: Sat, 14 Apr 2012 10:06:58 +0000
> From: Don Cox <[log in to unmask]>
> Subject: Re: Recording_78rpm_records/analog vs digital eq
>
> On 13/04/2012, George Brock-Nannestad wrote:
>
>
> > The so-called Nyquist criterion states that if you want to be able to
> > reconstruct a signal from a sampled representation of it, you have to
> > decide the highest frequency you want represented and then you have to
> > sample at a rate that is at least twice the highest frequency.
>
> Note, _at least_. It won't do any harm to go higher.
>
> > When
> > you then reconstruct your signal by providing voltages at the sample
> > rate according to the table of values that represents the audio
> > signal, you will have your full bandwidth and dynamic range back,
> > provided the resolution or bit-depth has been sufficient. It has been
> > claimed that this stepwise presented waveform makes the signal
> > unlistenable, but that is not the case, because you invariably smooth
> > it by filtering, so nothing above your defined highest frequency gets
> > out in the analog domain again. You will note that you are in full
> > control: define the maximum frequency and define the resolution. If
> > they are not sufficient to your purpose, go higher.
> >
>
> >
> > Now, we have a problem with pure sampling of a waveform: if it has a
> > frequency that is more than half of the sampling rate, that too will
> > be sampled, but in this case under-sampled, which means that the
> > result appears to be at a completely different and inharmonic and
> > jarring frequency, an alias. Once we have adopted a sampling frequency
> > we must simply ensure that no signal above half the sampling rate is
> > available for sampling.
> >
> It is interesting to see the digital photography community wrestling
> with these concepts. (Most cameras use optical anti-aliasing filters.)
>
> > This is done by filtering, so-called anti-alias filtering. With 44.1
> > kHz sampling rate, no signal above 22.05 kHz is permissible. On the
> > other hand, we do want our 20 kHz bandwidth - this is what a young,
> > pre-earbud ear can mostly hear.
>
> There seems to be good evidence that we can hear timing differences on
> impulse signals corresponding to much higher frequencies than the
> continuous sine waves normally used for testing hearing.
>
> > So, our filter has to go from full
> > transmission at 20kHz to zero transmission at 22.05 kHz *). No
> > problem, our telephone engineers have done this kind of exercise for
> > 90 years. However, such sharp cut-off filters come with some frightful
> > time delay distortion (phase to some), very audible down to 2 kHz.
> > That was the situation for about 10 years in CD audio, until someone
> > came up with the idea to correct the time response in the digital
> > domain by means of a digital filter. The currency to pay for this is
> > total delay time, but for something recorded a year ago, some
> > microseconds do not matter.
> >
> > In other words, many of our problems come from the filter. If we
> > increase the sampling rate we can make use of our more frequent
> > samples in two ways: we can do a gentler filtering that does not have
> > the delay effect at low frequencies, or we can increase our highest
> > frequency. If we do the latter, we shall be able to increase the time
> > resolution of our digital representation. With 20 kHz the maximum
> > slope of the waveform is only one quarter of that of an 80 kHz
> > bandwidth - reachable by a 192 kHz sampling frequency and a gentler
> > anti-aliasing filter.
> >
>
> >
> > A couple of other items came up while we were at 78rpm reproduction:
> >
> > - the reason why we need an elevated bandwidth for recordings on
> > rough surfaces is because that is where the noise signal is.
>
> This is the crucial point.
>
>
>
> > - one might consider that the pickup would be encountering a
> > formidable vertical wall when it met a square wave. However, the
> > recording is usually a velocity recording, that is the square
> > waveshape is differentiated (1st derivative), which means it turns
> > into a triangular wave. The problem is that with a high bandwidth, the
> > corners of this triangular wave (where the square shifts from constant
> > positive to constant negative and vice versa) are very sharp, and even
> > that may be difficult to trace. George Alexandrovich made a 7" test
> > record with a "square wave" - there are virtually no wiggles at the
> > corners of the triangles. It is for testing pickups, but I have not
> > dared to use it on anything but the ELP.
> >
> Back in the days when The Gramophone carried technical reviews of
> equipment, under John Borwick especially, oscilloscope traces of pickup
> cartridges playing "square waves" were shown in all reviews. I assume
> the actual waveforms on the LP were triangular.
>
>
> > - for the same reason a tick, modelled by a steep rise followed by
> > steep fall becomes two ticks, one positive and one negative.
> >
> > - even if you remove these two peaks and interpolate or draw a
> > waveform connecting the ends, the low frequency excitation of the
> > whole cartridge-tonearm system (stylus, cantilever, bearing, cartridge
> > mass, tonearm mass and resonances) still remains as a low-level thud -
> > a tail. CEDAR started back in 1988 with a program developed by Peter
> > Rayner while still at the British Library to remove not only the
> > ticks, but also the tail.
> >
>
> Regards
> --
> Don Cox
> [log in to unmask]
>
> ------------------------------
>
> Date: Sat, 14 Apr 2012 11:01:20 -0400
> From: "Richard L. Hess" <[log in to unmask]>
> Subject: Re: Recording_78rpm_records/analog vs digital eq
>
> Hi, Don,
>
> In the early 1970s, I recall getting into a long, and semi-heated
> discussion between two brands of cartridges. My colleague had done scope
> photos of various cartridges reproducing CBS Labs test records,
> including square waves. He said one cartridge was better than my
> favourite because it didn't show the ringing in the square waves. I said
> I didn't like his cartridge because it sounded dull and lifeless
> compared to my favourite which sounded more like live music.
>
> I also recall, a half decade or more later, a magazine, I think it was
> AUDIO Magazine, showed scanning electron micrographs (SEM images) of
> the grooves of one or more CBS Labs test records and the ringing showed
> up in the SEM images!
>
> Cheers,
>
> Richard
>
> On 2012-04-14 6:06 AM, Don Cox wrote:
> > Back in the days when The Gramophone carried technical reviews of
> > equipment, under John Borwick especially, oscilloscope traces of pickup
> > cartridges playing "square waves" were shown in all reviews. I assume
> > the actual waveforms on the LP were triangular.
>
> --
> Richard L. Hess email: [log in to unmask]
> Aurora, Ontario, Canada (905) 713 6733 1-877-TAPE-FIX
> http://www.richardhess.com/tape/contact.htm
> Quality tape transfers -- even from hard-to-play tapes.
>
> ------------------------------
>
> Date: Sat, 14 Apr 2012 16:54:15 +0000
> From: Don Cox <[log in to unmask]>
> Subject: Re: Recording_78rpm_records/analog vs digital eq
>
> On 14/04/2012, Richard L. Hess wrote:
>
> > Hi, Don,
> >
> > In the early 1970s, I recall getting into a long, and semi-heated
> > discussion between two brands of cartridges. My colleague had done
> > scope photos of various cartridges reproducing CBS Labs test records,
> > including square waves. He said one cartridge was better than my
> > favourite because it didn't show the ringing in the square waves. I
> > said I didn't like his cartridge because it sounded dull and lifeless
> > compared to my favourite which sounded more like live music.
> >
> > I also recall, a half decade or more later, a magazine, I think it was
> > AUDIO Magazine, showed scanning electron micrographs (SEM images) of
> > the grooves of one or more CBS Labs test records and the ringing
> > showed up in the SEM images!
> >
> That is funny. Make sure you are testing for what you think you are
> testing for. ;-)
>
> I would like to see those images.
>
> >
> > On 2012-04-14 6:06 AM, Don Cox wrote:
> >> Back in the days when The Gramophone carried technical reviews of
> >> equipment, under John Borwick especially, oscilloscope traces of
> >> pickup cartridges playing "square waves" were shown in all reviews. I
> >> assume the actual waveforms on the LP were triangular.
> >
> Regards
> --
> Don Cox
> [log in to unmask]
>
> ------------------------------
>
> End of ARSCLIST Digest - 13 Apr 2012 to 14 Apr 2012 (#2012-101)
> ***************************************************************
>
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