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* Origin: -= (I. SPECTRUM) =- (2:4623 / 55.68)
FIDO Echos (2:5063 / 47.11)
ZX.SPECTRUM
Msg: 2886 of 3160
From: Oleg Bashtenko 2:4623 / 55.68
Wed January 27, 1999 2:34
To: All Thu January 28, 1999 23:35
Subj: AY vs YM ...
Hello All!
AY 3-8910 or YM2149F?
The domestic market is saturated with music coprocessors
relatively cheap production in South-East. Widely
raspostraneny 40-pin microcontrollers
AY 3-8910 (AY) the production of Taiwan, and
as their Japanese counterparts YM2149F (YM)
firm Yamaha. With all the constructive
identity of these chips, yet students say more than "soft" and
"powerful" sound AY compared with YM. C On the other hand, in
some musical programs, reproduced through YM,
more noticeable stereo effect.
Search for the causes differences in sound led to the need to
investigate the characteristics of the analog outputs. As is
well known muzprotsessor (hereafter MP) contains three
independent D / A converter with logarithmic amplitude
characteristics of the channels A B, C. The logarithmic law of
change associated with the peculiarities of the perception of
the human ear volume. In Spectrum provided the work with
4-bit DAC, so the output volume has 16 steps and separated from
each other on the value of 3dB. Amplitude characteristics do
not depend on sound frequency, but depend on the load
resistance Rl. In this case, "myagkozvuchaschy" AY is the law
of distribution of the amplitudes are much more dissimilar to
"Ideal" than the YM. Dynamic range, ie ratio of maximum output
to minimum, for the AY is approximately 32dB, and for YM -
38dB. Flatness characteristics AY leads to a longer duration,
to be exact Volume poslezvuchaniya flowing sounds. The
difference is very noticeable when observing the effect of
diminishing the sound waveform. On the oscilloscope screen in
this case can be seen repeating peaks the distance between them
is filled with different amplitude levels at regular intervals.
And for AY has 16 spaces, which coincides with the reference
data, and for YM - 1932 period, ie amplitude effects for YM
formed 5-bit DAC!
And yet the "wrong" response
AY aurally perceived as longer poslezvuchanie, echo and unique
fusion of melodies. Last but not least role in such a
subjective assessment of play own musical compositions for the
Spectrum, which abound with passages varying in volume. YM
on hearing sounds more "dry", abruptly.
Here it is appropriate analogy with music
terms: for AY characteristic performance
melodies "legato" (a smooth transition of one
sound in the other) to YM - "staccato"
(Brief, jerky sound performance).
Question of the more "powerful" sound AY clarify study the load
characteristics of the analog outputs.
As applied in practice patterns load impedance of analog
outputs MP is 3 ... 6 ohms, so the melody through AY louder
than YM because of the higher output amplitude Umax. If the
load was less than 1, 8 ... 2 k, then the situation would change
on the opposite side, and YM would have sounded louder than AY.
The difference in the depth of the stereo due to different
internal resistance analog outputs AY and YM. In the initial
state without a signal and no load on
Each of the three outputs AY is zero stress, while the YM - a
constant level of 3 ... 3.2 V, which is exponentially decreases
to zero with decreasing load to short circuit. Analog MF
outputs are not afraid of short circuits in load. Short-circuit
current for YM reaches a considerable value 12 ... 15
mA. Analog outputs AY and YM are
schemes with an open emitter, ie, for
normal operation must be
galvanic connection with a total output
wire. As a sub-optimal solutions in Figure 1 shows the output
part of the MP connection to the computer "ATMTURBO-2".
Scheme 1
DD57A AY3-8910 (YM2149F)
4
A R17 * R21
R18 *> LEFT
3
B *
R19 *> RIGHT
38
C R20 * R22
R17, R20 = 1K
R18, R19, R21, R22 = 2,2 K
If you start to perform Beysikkomandu PLAY "V15A", in which
the coprocessor only plays the sound from channel A, and
measure the signal amplitude, entering the left and right
stereo channels, for AY in the scheme 1, the ratio of these
amplitudes of about 3 (9.5 dB), and YM - approximately 20
(26dB). Simultaneous getting signals left and right channels
obviously affects the stereo, which so softly pronounced
because of the summation signal on channel B. To improve the
channel separation in Figure 1 can change face values of
resistors R21 = R22 = 510 Ohms. The ratio of the amplitudes
will be more than 18dB, but with some decrease the output level.
For schemes with other resistors
should strive to ensure that the ratio of R17/R21 and R20/R22
more than 2. Scheme 1 change of face would be uncritical to the
type of applied magnetic field. If desired, to some extent
bring the sound YM AY possible to recommend a change
the slope of the amplitude characteristics of each of the three
channels and the introduction of the diodes trimming of
resistors on circuit 2. Trimmer to set the level at which will
be weakened in the amplitude of the upper steps of 6.5
hatakteristiki.
Scheme 2.
DD1 YM2149F out
>
4
A *
/
VD1 RP1
out
>
3
B *
/
VD2 * RP2 *
out
>
38
C *
/
VD3 * RP3 *
O +5 V
VD1-VD3 KD522B
RP1-RP3 = 1K
The signal is taken from the outputs (out) and then
mixed as in the corrected Figure 1.
Summarizing the research, there are two main aspects:
First, the circuit connecting the MP can
have different crosstalk between
stereo. In any case,
prehodnoe provide more damping
18 ... 20dB for all types of processors.
Secondly, the production of different MPs
countries and firms may have different amplitude
characteristics and, consequently, different nuances in the
sound of the same melodies.
RadioAmator 8 / 96
Oleg AKA 0lav
