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Exactly what I said RE a77. Or was that in a private mail? Shai בתאריך 04/15/12 3:49 PM, ציטוט Art Shifrin: > 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) >> *************************************************************** >> -- בברכה, שי דרורי מומחה לשימור והמרה של אודיו וידאו וסרטים 8-35 ממ.