spectrum. Figure 7 shows frequency response measurements
for minimum and maximum gain. The curves are quite linear
– as to be expected – and only start to drop slightly below
20 Hz. At a sampling rate of 48 kHz the upper end of the curve
reaches up to 24 kHz (with all faders in the 0 dB position). This
results in a gain of +1.34 dB plus +3 dB due to the Pan set-
ting. The –6 dB preamp setting thus amounts to a value
of –1.66 dB.
place digitally. Figure 4 shows the process of analog gain trim
in 6 dB intervals before the A/D converter and the digital gain
trim in 1 dB intervals after the A/D converter.
To measure the preamp noise with ADC, a digital gain of 20 dB
was set (and subtracted from the measured value later).
So, the input section noise can be measured independently
from the output section. At the lowest gain setting the maxi-
mum level can be +32 dBu and, accordingly, at the highest gain
setting –40 dBu. At the lowest gain an excellent signal-to-noise
ratio of 110 dB is achieved by the A/D converter. In case of
higher gain values the preamp noise will dominate (but, at the
maximum gain of +66 dB, 86 dB can still be achieved).
Based on these figures, the equivalent input noise will be –126
dBu. The corresponding interference spectra (figure 6) show a
clean white noise. Including the additional 20 dB gain, the over-
all noise level is –65, respectively –41 dBu. If you then subtract
the 20 dB, the corresponding values will be –85 and –61 dBu.
The maximum output voltage at the analog outputs amounts
to +25 dBu, resulting in dB S/N values of 110, respectively 86.
A separate calculation of the analog output values of the
Yamaha TF1 results in an S/N of 111 dB (linear) and of 113 dB (A)
noise levels.
The measuring (as in figure 6) was performed with the master
fader down. There is only uncritical white noise in the noise
6
|
PRODUCTION PARTNER
09/2015
Test
| Yamaha TF
Noise spectrum
at the output in dBu at max. (red) and minimum
(blue) preamp gain, measured at the analog output in dBu with ad-
di20 dB digital gain (figure 5)
Noise spectrum
at the analog output with fader down at an over-
all level of –86 dBu (lin) and –89 dBu (A). The maximum output vol-
tage repr25 dBu (figure 6)
Frequency response
measured through everything from the ana-
log input to the analog output at a minimum gain of –6 dB (red)
and a maximum gain of +66 dB (blue) (figure 7)
