Digital delay og vinylgravering

[tkr]

Fra Wikipedia:

A digital delay line is a discrete element in digital filter theory, which allows a signal to be delayed by a number of samples. If the delay is an integer multiple of samples, digital delay lines are often implemented as circular buffers. This means that integer delays can be computed very efficiently.

The delay by one sample is notated

and delays of

samples is notated as

motivated by the role the z-transform plays in describing digital filter structures.


Kjedelig? Kanskje litt mer interessant når jeg tar med dette:

It would be a good idea to explain why the digital delay line is commonly used in vinyl cutting these days:

When a master lacquer is cut, the engineer must do the entire LP side at once, without stopping. If (when) a mistake is made with levels, EQ, etc, the lacquer is discarded, and the engineer starts over with a new blank. This gets expensive.

It is necessary for the engineer to monitor the program before it is cut, so that changes in level and EQ can be anticipated and adjusted for in time. However, the cutting stylus itself cannot be used for monitoring, as this signal is too late in the chain. (sound has already been recorded on the lacquer before it can be played back. Too late for the engineer to make any changes.)

Therefore, it is necessary to have some kind of "early playback" so that the engineer can make changes in time. In the past, custom analog mastering decks had a "preview head" mounted in the tape path, usually on the left side of the deck plate, near the supply reel. The tape path was modified with extra rollers and guides so that the tape would pass over the preview head (one second or so) before it got to the "normal" playback head for cutting. Quite a complex system to allow the engineer to monitor the signal before making the cut.

Keep in mind that a "normal" pro half-track deck may cost between 10 and 15 grand. Now add the cost of the custom mods and the preview head. Add in the popularity of 30 ips mastering, which complicates the tape path further, in order to get enough delay time between the preview and playback heads. Add in the rise of digital technology, and it wasn't long before some bright soul found an easier way to delay the signal, before sending it to the cutting stylus.

I would guess that the use of a digital delay line in cutting vinyl was common by the mid-1990s, as vinyl became a small-market niche product, and boutique labels no longer had access to custom mastering decks and other tools of the major-label process.

M.a.o. har signalet til nesten all vinyl de siste 25- 30 årene vært gjennom en AD/DA loop på tur mellom analog master og rillegravering.

mvh

 

[tkr]

Ehhh, javel, og hva så ???

Vel, da vil frekvensinnholdet på vinylen oppad være begrenset til halve samplingsfrekvensen, dvs max 22,05 kHz. ved 44.1 kHz.

mvh

 

[tkr]

Konvertering av bass til monosignal

Steve Berson:

Most of the Neumann Elliptical Equalizers I've seen had selectable crossover freq's of either 75 & 150 or 150 & 300Hz. For most of the 12" singles I cut to max possible level I would usually have to set the EE to 150Hz, and occasionally up to 300Hz . For LP's though unless there was specific problems it's often easy not to have to have an EE on at all.

The only company I know of making EE's currently is ADT.

Besides an EE the other processor used to mono the bass end is the Vertical Amplitude Limiter - which instead of mono-ing everything under the crossover point instead mono's at a variable crossover point based on having a set limit of the vertical movement of the cutting head - i.e. it would only mono the bass at the points where things were out of phase beyond the set threshold. The Neumann VAB-84 that I got to use in the old Europadisk desk was often a bit more transparent sounding than having an EE clamp on everything.

For really out of phase material sometimes you not only need to have an EE and a VAL on but also lower the level being sent to the cutting head.

mvh

 

[Cobra2]

Noen "ny"-pressinger sendt i skammekroken: hall of shame :
Better Records: Hot Stamper LPs -- 100% Guaranteed Great Sound.

 

[tkr]

Noen "ny"-pressinger sendt i skammekroken: hall of shame :
Better Records: Hot Stamper LPs -- 100% Guaranteed Great Sound.

Flott link, takker!

mvh

 

[ottone]

Digital delay er greit nok det. Men det må jo ikke være 44kHz sampling? Jeg ville tro og forvente at man bruker noe høyere i mastring, men ingenting overrasker.
På nye opptak er vel selve masteren også digital fra start, men hvis master er en gammel analog tape, er det så vanskelig å gjøre det på samme måten som før?

Personlig tenker jeg bare: men man kjøper da vel ikke vinyl som er mindre enn 30 år gammel?
-Jo, innrømmer et par kjøp fra 2L og HiQ, alt må jo prøves, men det blir nok med det.

 

[atlechri]

Masterdisk skriver eksplisitt at de ikke bruker delay line, men ekstra lydhode når de mastrer fra analog tape ;-)

Masterdisk: Over 35 Years of Vinyl Mastering | The Masterdisk Record
Mvh

 

[atlechri]

Og de skriver at de ikke er de eneste.

 

[tkr]

Digital delay er greit nok det. Men det må jo ikke være 44kHz sampling? Jeg ville tro og forvente at man bruker noe høyere i mastring, men ingenting overrasker.

All literatur jeg har kommet over nevner 44.1, har ikke kommet over noe annen samplingsfrekvens. Bitdybde varierer, dog, og de første DDLene hadde en bitdybde på 8, om jeg ikke husker feil.

På nye opptak er vel selve masteren også digital fra start, men hvis master er en gammel analog tape, er det så vanskelig å gjøre det på samme måten som før?

De aller, aller fleste mastertapene er numera i så dårlig forfatning at de forlengst er overført til digitalfiler.

Personlig tenker jeg bare: men man kjøper da vel ikke vinyl som er mindre enn 30 år gammel?
-Jo, innrømmer et par kjøp fra 2L og HiQ, alt må jo prøves, men det blir nok med det.

Noen av oss har allerede kjøpt 30-40 år gammel vinyl for 30- 40 år siden.

mvh

 

[tkr]

Og de skriver at de ikke er de eneste.

- Jeg skriver da også at de aller fleste, ikke alle, moderne LPer har innom en AD/DA- loop.

mvh

 

[tkr]

Just to prove a point frekvensanalyse av Beatles` "I want to hold your hand" fra "Love":

Tydelig bråbrems rundt ca. 20 kHz. Har nok vært innom 44.1 kHz AD/DA .

mvh

 

[tkr]

Mer fra Wikipedia:

Noise performance

For electronic audio signals, sources of noise include mechanical, electrical and thermal noise in the recording and playback cycle. The actual process of digital conversion will always add some noise, however small in intensity; the bulk of this in a high-quality system is quantization noise, which cannot be theoretically avoided, but some will also be electrical, thermal, etc. noise from the analog-to-digital converted device.
The amount of noise that a piece of audio equipment adds to the original signal can be quantified. Mathematically, this can be expressed by means of the signal to noise ratio (SNR or S/N). Sometimes the maximum possible dynamic range of the system is quoted instead. In a digital system, the number of quantization levels, in binary systems determined by and typically stated in terms of the number of bits, will have a bearing on the level of noise and distortion added to that signal. The 16-bit digital system of Red Book audio CD has 2¹⁶= 65,536 possible signal amplitudes, theoretically allowing for an SNR of 98 dB. Eachadditional quantization bit adds 6 dB in possible SNR, e.g. 24 x 6 = 144 dB for 24 bit quantization, 126 dB for 21-bit, and 120 dB for 20-bit.

With digital systems, the quality of reproduction depends on the analog-to-digital and digital-to-analog conversion steps, and does not depend on the quality of the recording medium, provided it is adequate to retain the digital values without error.

Analog systems

Consumer analog cassette tapes may have a dynamic range of 60 to 70 dB. Analog FM broadcasts rarely have a dynamic range exceeding 50 dB, though under excellent reception conditions the basic FM transmission system can achieve just over 80dB. The dynamic range of a direct-cut vinyl record may surpass 70 dB. Analog studio master tapes using Dolby-A noise reduction can have a dynamic range of around 80 dB.