The Tube Used In The Ultragain Pro - Behringer MIC2200 User Manual

6
ULTRAGAIN PRO MIC2200 User Manual
1.2.2 What are audio dynamics?
A remarkable feature of the human ear is that it can detect the most wide
ranging amplitude changes—from the slightest whisper to the deafening roar
of a jet-plane. If one tried to record or reproduce this wide spectrum of sound
with the help of amplifiers, cassette recorders, records or even digital recorders
(CD, DAT etc.), one would immediately be restricted by the physical limitations of
electronic and acoustic sound reproduction technology.
The usable dynamic range of electro-acoustic equipment is limited as much
at the low end as at the high end. The thermal noise of the electrons in the
components results in an audible basic noise floor and thus represents the
bottom limit of the transmission range. The upper limit is determined by the
levels of the internal operating voltages; if they are exceeded, audible signal
distortion is the result. Although in theory, the usable dynamic range sits
between these two limits, it is considerably smaller in practice, since a certain
reserve must be maintained to avoid distortion of the audio signal if sudden level
peaks occur. Technically speaking, we refer to this reserve as "headroom"—
usually this is about 10 - 20 dB. A reduction of the operating level would allow for
greater headroom, i.e. the risk of signal distortion due to level peaks would be
reduced. However, at the same time, the basic noise floor of the program material
would be increased considerably.
P/dB
140
120
100
80
60
40
Fig. 1.1: The dynamic range capabilities of various devices
It is therefore useful to keep the operating level as high as possible without
risking signal distortion in order to achieve optimum transmission quality.
P/dB
+20
Headroom
0
-20
-40
-60
-80
Fig. 1.2: The interactive relationship between the operating level and the headroom
Clipping
Operating level
E ective SNR
Noise oor
t

1.3 The tube used in the ULTRAGAIN PRO

A closer look at developments and trends in audio technology shows that tubes
are enjoying a renaissance today, in a time when even amateur musicians are free
to use digital effects processors and recording media, and ever more affordable
digital mixing consoles are becoming a natural part of the equipment of many
semi-professional studios. Manufacturers try with ever new algorithms to get the
most out of DSP's (Digital Signal Processors), the heart of any digital system.
Still, many audio engineers, particularly old hands often prefer using both old
and new tube-equipped devices. As they want to use their warm sound character
for their productions, they are ready to accept that these "little darlings"
produce a higher noise floor than modern, transistor-based devices. As a
consequence, you can find a variety of tube-based microphones, equalizers,
preamps and compressors in today's recording and mastering environments.
The combination of semiconductor and tube technologies gives you the
additional possibility of using the best of both worlds, while being able to make
up for their specific drawbacks.
1.3.1 Tube history
Due to many patent litigations, it is difficult to determine exactly when the tube
was "born". First developments in tube technology were reported between
1904 and 1906. It was a research task of that time to find a suitable method for
receiving and rectifying high frequencies. On April 12, 1905, a certain Mr. Fleming
was granted a patent for his "hot-cathode valve" which was based on Edison's
incandescent lamp. This valve was used as a rectifier for high-frequency signals.
Robert von Lieben was the first to discover (probably by chance) that the anode
current can be controlled by means of a perforated metal plate (grid)—one of
the milestones in the development of amplification tubes. In 1912, Robert van
Lieben finally developed the first tube for the amplification of low-frequency
signals. Initially, the biggest problem was to produce sufficient volume levels,
which is why resonance step-ups (though impairing the frequency response)
were used to maximize the attainable volume. Later, the objective was to
optimize the electroacoustic transducers of amplifiers in such a way that a broad
frequency band could be transmitted with the least distortion possible.
However, a tube-specific problem is its non-linear amplification curve, i.e.
it modifies the sound character of the source material. Despite all efforts to
ensure a largely linear frequency response, it had to be accepted that tube
devices produce a "bad" sound. Additionally, the noise floor generated by the
tubes limited the usable dynamics of connected storage media (magnetic tape
machines). Thus, a one-to-one reproduction of the audio signal's dynamics
(expressed as the difference between the highest and lowest loudness
levels of the program material) proved impossible. To top it all, tube devices
required the use of high-quality and often costly transducers and sophisticated
voltage supplies.
With the introduction of semiconductor technologies in the field of audio
amplification, it soon became clear that the tube would have to give way to
the transistor, as this device featured an enormously enhanced signal-to-noise
ratio, required a less complex power supply and yielded an improved frequency
response. Plus, semiconductor-based circuits can be realized much more easily—
for less money.
Two decades later, the introduction of binary signal processing meant the
beginning of a new era of recording media that provided plenty of dynamic
response and allowed for the loss-free copying of audio signals. As digital media
were enhanced, however, many people began to miss the warmth, power and
liveliness they knew from analog recordings. This is why purists still today
consider digital recordings as "sterile" in sound.