|
|
This topic comprises 5 pages: 1 2 3 4 5
|
|
Author
|
Topic: 78's
|
|
|
Leo Enticknap
Film God
Posts: 7474
From: Loma Linda, CA
Registered: Jul 2000
|
posted 12-31-2006 06:41 AM
quote: Phil Hill
I would think since the RIAA recording curve attenuates the low freq up to about 20dB at 20 Hz and boosts the HF at 20kHZ about 20dB, that the playback without RIAA EQ would be VERY "bright" and not flat.
I've never tried playing RIAA-equalised vinyl through a non-RIAA preamp (e.g. the mic input of a PC sound card), but that's exactly what I'd expect to happen, too - lots of HF, nowhere for the surface noise to hide and muddy, indistinct bass. By the same token, when you play a record with a less severe EQ curve to RIAA (e.g. a Blumlein or Westrex 78) through an RIAA preamp, you get loud, rumbling bass and a reduction in high-end surface noise, but at the expense of grossly amplified midrange surface noise (which means that records which had an abrasive agent added to the shellac mix in order to grind down steel needles to the groove seats, e.g. inter-war HMVs, sound absolutely horrid) and most of the HF signal being totally lost. On an orchestral track or a male singer it can sound OK, but piano solos or female singers played this way sound hideous.
| IP: Logged
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Mark Gulbrandsen
Resident Trollmaster
Posts: 16657
From: Music City
Registered: Jun 99
|
posted 01-03-2007 07:00 PM
Perhaps this explanation will help out......
"RIAA equalization is a specification for the correct playback of vinyl records, established by the Recording Industry Association of America. The purpose of the equalization is to permit greater playback times, improve sound quality, and to limit the physical extremes that would otherwise arise from recording analogue records without such equalization.
The RIAA equalization curve has operated as a de facto global industry standard for the recording and playback of vinyl records since 1954. Prior to that time - mainly between 1940 and 1954 - each record company applied its own equalization; there were over 100 combinations of turnover and rolloff frequencies in use, the main ones being AES, LP, NAB and FFRR.
Before 1940, most records were cut flat, with a low-pass turnover of 6 dB/octave below 300 Hz to 800 Hz. This included broadcast recordings (transcriptions) and motion picture recordings before sound-on-film. If you play a pre-WWII 78rpm record through a modern preamp, you will effectively be playing it with a scratch filter whose cutoff begins at 2200 Hz, giving lack of high frequencies and muffled voices.
RIAA equalization is a form of preemphasis on recording, and deemphasis on playback. A record is cut with the low frequencies reduced and the high frequencies boosted, and on playback the opposite occurs. The result is a flat frequency response, but with noise such as hiss and clicks arising from the surface of the medium itself much attenuated. The other main benefit of the system is that low frequencies, which would otherwise cause the cutter to make large excursions when cutting a groove, are much reduced, so grooves are smaller and more can be fitted in a given surface area, yielding longer playback times. This also has the benefit of eliminating physical stresses on the playback stylus which might otherwise be hard to cope with, or cause unpleasant distortion.
A drawback of the system is that rumble from the playback turntable's drive mechanism is greatly amplified, which means that players have to be carefully designed to avoid this.
RIAA equalization is not a simple low-pass filter. It carefully defines transition points in three places - 75 µs, 318 µs and 3180 µs, which correspond to 2122 Hz, 500 Hz and 50 Hz. Implementing this characteristic is not especially difficult, but more involved than a simple linear amplifier. The phono input of most hi-fi amplifiers have this characteristic built-in, though it is omitted in many modern designs due to the gradual obsolescence of vinyl records. A solution in this case is to buy a special preamplifier which will adapt a magnetic cartridge to a standard line-level input, and implement the RIAA equalization curve separately. Some modern turntables feature built-in preamplification to the RIAA standard. Special preamps are also available for the various equalization curves used on pre-1954 records."
Some of you might also be interested in Norm Schneiders phono remastering equalizer that is available from Smart Devices
Mark
| IP: Logged
|
|
Charles Greenlee
Jedi Master Film Handler
Posts: 801
From: Savannah, Ga, U.S.
Registered: Jun 2006
|
posted 01-03-2007 08:22 PM
Yes, Mark, it was already posted on the first page or 2, but quite worthy of being reposed, as well are some of the other devices previously posted. I would "run out and grab one" immediatly, but I'm not paid much better than floor employees, yet.
Btw, on a side note. If I didn't mention it before. I withdrew my resignation, and am working things out. In fact, I just dropped my second job and came on full time at the theatre, though at an overall paycut. But hopefully I can get back on tack with my jedi training, and move up to "Sound Technitian" Hopfully, not being around those crashing pins constantly will restore the suffering part of my hearing.
I have gotten more parts to work on my laser turntable, maybe make it self guiding. For now, the laser actually "reads" the track, but the tone arm is still guided by the stylus. And for now, it's mono only, and suffers from cross talk, whcih better alginment, and a slef guiding head should help a bunch.
| IP: Logged
|
|
|
|
|
|
|
|
|
|
|
|
|
|
All times are Central (GMT -6:00)
|
This topic comprises 5 pages: 1 2 3 4 5
|
Powered by Infopop Corporation
UBB.classicTM
6.3.1.2
The Film-Tech Forums are designed for various members related to the cinema industry to express their opinions, viewpoints and testimonials on various products, services and events based upon speculation, personal knowledge and factual information through use, therefore all views represented here allow no liability upon the publishers of this web site and the owners of said views assume no liability for any ill will resulting from these postings. The posts made here are for educational as well as entertainment purposes and as such anyone viewing this portion of the website must accept these views as statements of the author of that opinion
and agrees to release the authors from any and all liability.
|
Home
![[Smile]](smile.gif)
![[thumbsup]](graemlins/thumbsup.gif)
Printer-friendly view of this topic