background image

higher frequencies. Upon playback, the
level of the treble is reduced; the
higher the frequency the lower the
output. This reduces the problem of
noise caused by surface dirt on the
disc, however it would also reduce the
high frequency content of the audio
signal itself. This is counteracted by
increasing the level of the
high-frequency portion of the audio
signal when it is mastered for the disc.

This general idea of lowering the level
of low-frequencies and/or boosting
highs when recording and doing the
opposite upon playback is a very old
idea in the audio industry and has been
used on many formats ranging from
film “talkies” to early compact discs.
Unfortunately, however, di

erent

recording companies and studios used
di

erent filters on phonographs for

many years.

2

Finally, in the mid-1950s,

the Recording Industry Association of
America (the RIAA) suggested a
standard filter description with the
intention that it would be used
world-wide for all PVC “vinyl” records.

Figures

2.4

and

2.5

show the responses

of the RIAA filters used in both the
mastering and the playback of long
playing vinyl records. Although there
are other standards with slightly
di

erent responses, the RIAA filter is

by far the most commonly-used.

Figure 2.4: The “pre-emphasis” filter to

be used in the mastering to disc, as

described by the RIAA standard. The

black line shows the simplified descrip-

tion, and the red curve shows the real-

world implementation.

Figure 2.5: The “de-emphasis” filter to

be used for playback as described by

the RIAA standard. This standard filter

response is integral in what is now com-

monly called a “RIAA preamp”.

It may be of interest to note that
typical descriptions of the RIAA
equalisation filter define the transition
points as time constants instead of
frequencies. So, instead of 50 Hz, 500
Hz, and 2122 Hz (as shown in the
response plots), the points are listed as
3180

µ

s, 318

µ

s, and 75

µ

s instead. If

you wish to convert a time constant
(Tc) to the equivalent frequency (F),
you can use the equation below.

F = 1 / (2

π

Tc)

2.3 Mono to Stereo

In Edison’s first cylinder recordings, the
needle vibrated up and down instead
of left and right to record the audio
signal. This meant that the groove cut
into the surface of the tin foil was
varying in depth, and therefore in
width, as shown in Figure

2.6

.

Figure 2.6: Example of an audio sig-

nal encoded using a vertical cutting sys-

tem.

There are some disadvantages to this
system, such as the risk of the needle

slipping out of the groove when it is
too shallow, or su

ering from

excessive wear if the groove is too
deep. In addition, any vertical variation
in the recording surface (such as a
cylinder that is not quite round, or
mechanical vibrations in the player
caused by footsteps in the room)
becomes translated into unwanted
noises upon playback.

3

Figure 2.7: An Edison cylinder player, on

display in the Struer Museum.

Figure 2.8: A closeup of the Edison

player.

Notice that the needle is

mounted to move vertically, modulating

a membrane located at the end of the

tonearm (the bent pipe).

Berliner’s Gramophone used a di

erent

system, where the needle vibrated
sideways instead. This lateral cut
system produced a groove on the disc
with a constant depth, thus avoiding
some of the problems incurred by the
vertical cut recording system.

Figure 2.9: Example of an audio signal

encoded using a lateral cutting system.

2

see the Manual of Analogue Sound Restoration Techniques (2008), by Peter Copeland

3

Some 78 RPM discs use a vertical cutting system as well, including those made by Edison Disc Records and Pathé.

5

Содержание Beogram 4000c

Страница 1: ...Beogram 4000c Technical Sound Guide Bang Olufsen A S This manual is for information purposes only and is not legally binding November 27 2020...

Страница 2: ...ross 7 3 2 Signal Levels 8 3 3 Tip shape 10 3 4 Bonded vs Nude 12 3 5 Tracking force 12 3 6 E ective Tip Mass 12 3 7 Compliance 13 3 8 Soundsmith SMMC20CL 13 4 Audio Specifications 14 4 0 1 Magnitude...

Страница 3: ...Emil Berliner was awarded a patent for a sound recording and reproducing system that was based on a groove in a rotating disc rather than Edison s cylinder the original version of the system that we k...

Страница 4: ...are the same at Time 0 ms However it is also evident that when this is true they have very di erent amplitudes in fact the amplitude would have to double for every halving of frequency a drop of 1 oc...

Страница 5: ...ns of the RIAA equalisation filter define the transition points as time constants instead of frequencies So instead of 50 Hz 500 Hz and 2122 Hz as shown in the response plots the points are listed as...

Страница 6: ...down left up right for example This means that signals that are identical in both channels move the stylus laterally exactly as in earlier monophonic discs 4 Figure 2 10 An over simplified depic tion...

Страница 7: ...eophonic Transducer Cartridge In 1963 Erik R rbaek Madsen of Bang Olufsen filed a patent for a cartridge based on the Moving Iron principle In it a cross made of Mu metal is mounted on the stylus Each...

Страница 8: ...be encoded without incurring additional distortion that is inherent in the encoding system itself is when the maximum or minimum value in the audio signal reaches the highest possible signal value of...

Страница 9: ...here is a relationship between the total playing time of a vinyl disc and the modulation velocity In order to have 20 minutes of music on a 12 LP spinning at 33 1 3 RPM then it the standard method was...

Страница 10: ...here are a number of options when choosing the shape of the playback stylus 3 3 Tip shape The earliest styli were the needles that were used on 78 RPM gramophone players These were typically made from...

Страница 11: ...k deeper into the groove making it more di cult for it to move independently on the two audio channels The second is that the point of contact between the stylus and the vinyl becomes smaller which ca...

Страница 12: ...pin which is in turn connected to the cantilever the long arm that connects back to the cartridge housing This bonded design is cheaper to manufacture but it results in a high mass at the stylus tip...

Страница 13: ...the compliance of the stylus suspension Compliance is the opposite of spring sti ness the more compliant a spring is the easier it is to compress and the less it pushes back Like many other stylus pa...

Страница 14: ...of 70 7 mm sec 4 0 3 Rotational speed Every recording playback system whether for audio or for video signals is based on the fundamental principle that the recording and the playback happen at the sam...

Страница 15: ...changes in the speed that are higher than 100 Hz This is typically only a problem with analogue tape decks caused by the magnetic tape sticking and slipping on components in its path and is not often...

Страница 16: ...nal relative to the average frequency however the e ect of very slow and very fast changes have been reduced by the filter Finally the standard deviation of the variation from the average is calculate...

Страница 17: ...mith SMMC20CL Stylus Nude 0 12 mm square Radius of curvature Contact Line Recommended tracking force 1 3 g Compliance 28 m mN E ective tip mass 0 32 mg General information Automatic speed selection Ye...

Страница 18: ...nditions in the Cutting and Playing of Stereo Disk C R Bastiaans Vol 11 Issue 1 Jan 1963 Factors A ecting the Stylus Groove Relationship in Phonograph Playback Systems C R Bastiaans Vol 15 Issue 4 Oct...

Страница 19: ...commendations for Lateral Cut Commercial and Transcription Disk Recordings 98 Processed Disk Records and Reproducing Equipment 386 Method of Measurement of Speed Fluctuations in Sound Recording and Re...

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