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Audio ICs
High-definition sound processor
BA3884F / BA3884S
The BA3884F and BA3884S are sound processor ICs that perform phase and harmonic compensation on audio signals
to accurately reproduce the “rise” section of audio signals that determines the characteristics of the sound, and thus
reproduce the original recording as naturally as possible.
Applications
Component stereo systems, radio cassette players, car
stereo systems, televisions, VCRs, multimedia PCs,
computer game machines and karaoke machines.
Features
1) Corrects distortion in the rising section of audio signals that results from miss-matched speakers and
amplifiers, and reproduces the original sound faithfully.
2) To allow application with all types of speakers and
sources, the clarity can be adjusted using DC control.
3) DC control provided for selection of either processor
mode or bypass mode.
4) Bass boost can be adjusted with the DC control in order to maintain a good balance with the dynamically
changing upper frequencies.
Absolute maximum ratings (Ta = 25C)
Recommended operating conditions
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Audio ICs BA3884F / BA3884S
Block diagram
Electrical characteristics (unless otherwise noted, Ta = 25C, V
Electrical characteristics (R
L = 100kΩ, VCTL1 = 4.5V and VCTL2 = 4.5V)
CC = 9V, fIN = 1kHz, VIN = 200mVrms, Rg = 600Ω,
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Audio ICs BA3884F / BA3884S
Measurement circuit
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Audio ICs BA3884F / BA3884S
Circuit operation
The BA3884F / S high-definition sound processor system IC treats the amplifier and speakers as a total audio
system, and performs signal processing at the amplifier
input stage to accurately reproduce the rise sections of
audio signals that determine the characteristics of sound,
and ensure that the replayed audio is as close to the original sound and as natural sounding as possible.
Problems relating to playback of sound on audio systems.
With naturally-generated sound, high-frequency harmonic components generally occur first, followed by the
fundamental frequency components. This also applies to
the attack section of the sound that characterizes many
musical instruments. It is the amplitude component that
gives form to the frequency component and envelope at
the rising point of sound, and this expresses the characteristics of the sound. Therefore, when replaying audio
on audio playback systems, it is extremely important that
Operating principle
To solve the problems described above, the BA3884F / S
performs the audio signal processing described below.
the rise section of the signal be expressed accurately
with respect to the original sound.
However, there is inevitable mismatching between the
speakers and amplifiers in current audio systems. Solidstate power amplifiers use negative feedback techniques
and operate off a fixed voltage supply, but as speakers
are a current element, mismatching in the system inevitably occurs. In addition, the speaker impedance characteristics are strongly influenced by the electrical reactance of the voice coil, and the mechanical reactance of
the cone assembly. As a result of this, distortion is generated in the rising sections of audio signals, causing
phase shift in the reproduced sound. In addition, impedance increases in the treble region which reduces the
speaker amplitude and reduces the harmonic component, and as a result there is a tendency to masking of
large mid-frequency signal components that follow, and
this makes it difficult to reproduce the rising sections of
the sound.
Phase shift compensation
The input signal is separated into three regions : bass
(20Hz to 150Hz), middle (150Hz to 2.4kHz) and treble
(2.4kHz to 20kHz). These regions are then joined again
with the middle and treble regions phase shifted -180
and -360 respectively with respect to the bass signal.
This phase shift adjusts the delay time characteristic for
each band and minimizes the distortion of the rising section of the audio signal.
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Audio ICs BA3884F / BA3884S
Amplitude compensation (harmonic compensation)
To maintain appropriate auditory balance for the treble
region that is made up of harmonic components, a highspeed detector and high-performance VCA circuit are
used for amplitude control of the treble component. The
amount of compensation is determined from a calculation performed based on the DC level input to the CTL1
pin, and the DC level detected from the input signal. The
internal control signal obtained from this calculation compensates the amplitude of the treble component input to
the VCA. This amplitude compensation recovers the harmonic component, and improves the reproduction clarity
(definition level) of instruments and vocals.
Bass boost
T o maintain good balance with the dynamically changing
treble component it is possible to boost the bass component. The amount of bass boost is determined by the DC
level applied to CTL2.
External components
The frequency characteristic in processing mode with
maximum definition level and maximum bass boost is
given below.
Mode switch
The DC voltage on the CTL pin can be used to switch the
IC between processing mode and bypass mode. When
processing mode is selected, the audio signal is enhanced using the compensation circuits described above
before being output. When bypass mode is selected, the
signal bypasses all of the compensation circuits, and
only passes through a buffer amplifier before output.
As indicated in the diagram, capacitors C1 and C2 determine the treble component cutoff frequency. By varying
the values of these components, the frequency characteristic can be changed as indicated by the dotted line in
the diagram. This varies the balance of the harmonic
component, and is an important factor in determining the
tone quality.
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C1 :External capacitor connected
between the VCA and MIX pins
(0.068µF in the application
circuit).
C2 :External capacitor connected
between the OUT and MIX pins
(470pF in the application
circuit).
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Audio ICs BA3884F / BA3884S
Control table
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Audio ICs BA3884F / BA3884S
Application example
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Operation notes
(1) Control pin (CTL)
The level of the DC voltage applied to the control pin
should be in the range 0V to V
may not be possible in the region of the threshold voltage. Allow sufficient margin when setting this voltage.
(2) Recommended operating range
Provided the IC is operated within the operating temperature range and within the recommended operating conditions, the general circuit functions are guaranteed to operate correctly, and there will not be significant changes
in the electrical characteristics.
(3) Application example circuit
Provided the circuit constants in the application example
CC. Appropriate switching
circuit are used, the application circuit should function
correctly. However , we recommend that you confirm the
characteristics of the circuit in actual use, and take note
of the cautionary items described above. If you change
the circuit constants, check both the static and transient
characteristics of the circuit, and allow sufficient margin
to accommodate variations in both the IC and the external components.
(4) License
This IC is manufactured under license from BBE Sound
Inc. (U.S.A.). A license agreement with BBE Sound Inc.
is required to use this component.
Electrical characteristics curves
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Audio ICs BA3884F / BA3884S
External dimensions (Units: mm)
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