Belar FMHD-1, Operator'S Manual

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FMHD-1 Operator’s Manual
BELAR ELECTRONICS LABORATORY, INC. Page 21
The two bars in the middle of the screen indicate the amplitude and timing relationships between the main
analog and digital signals. For both amplitude and timing, the red indicator shows a short-term value of
the respective error, and the wider yellow bar shows long-term averaged errors.
The upper bar shows the relative amplitude of the analog and digital L+R signals, approximately the
loudness perceived by a listener. The error in relative amplitude in indicated over a range of ±20.0dB,
with a resolution of 0.1dB. Listeners can detect differences of about one decibel, so it is best to keep the
amplitudes within about ±1.0dB. Differences in the way the analog and digital program audio is
processed will make level matching more difficult.
The lower bar shows the time alignment between the main analog and digital audio programs. It is
metered in increments of 22.68 microseconds, or the sample period of 44.1-kHz digital audio streams.
The range of indication is ±16,384 samples, or ±371.5 milliseconds. This time relationship is adjusted in
the HD encoder/processor at the transmitter.
To improve resolution of the timing error, the “
HR
” setting (for horizontal resolution) may be adjust for
full-scale timing error indications of ±256 samples, or ±5.8 milliseconds. Depress the encoder knob
momentarily activate the cursor on the screen. Press a second time to highlight the HR reading in green.
Rotate the encoder knob to set the timing error resolution.
The upper-left corner of the display has a “
Polarity
” indicator. When green, the analog and digital
audio signals have the same relative waveform polarity. If the indicator is red, the analog and decoded
digital waveforms are 180 degrees out of phase. With perfect time alignment, an audio phase reversal
will cause at near cancellation of audio at the receiver output at some point in the analog-digital blending
process. With timing errors, the cancellation can produce undesirable effects in the audio. This condition
should be corrected somewhere in the audio chain ahead of the analog or HD exciters.
Quick visual confirmation of proper hybrid setup is afforded by a green polarity indication and two red
and yellow indicators at the centers of the two graphs on this screen.
5.7 Program Selection Screen
The Program Selection Screen indicates which of the eight possible digital program streams are present in
the received IBOC HD broadcast and which digital decoders are processing those streams. The program
types carried by each digital program stream are identified by numeric code and descriptive text. Decoder
selections and assignments may be made in this screen using the rotary encoder.
The eight possible HD program streams are listed in the column along the left side of the screen: “
HD1
”
through “
HD8
”. (
HD1
is the Main HD program, and “
HD2
” through “
HD8
” correspond to Supplemental
Programs 1 through 7.) Columns two and three of the display indicate the program type by numerical
code and descriptive text, respectively.
The data block on the right-hand side of the display has four columns of enunciators, eight enunciators to
a column. The four columns individually correspond to the four HD™ decoders, designated “
D1
”
through “
D4
”, possibly incorporated in an FMHD-1 . The right-hand data block essentially represents a
switching matrix indicating the availability, unavailability, or the selection of a program data stream as an
HD decoder input. An enunciator lit yellow or green indicates a program stream is available. A green
enunciator indicates the HD decoder marked at the top of the respective column is assigned to the audio
program stream marked at the extreme left of the respective row. Any audio programs marked green in
this screen are available for output to the Audio Bargraph Screen and the XLR, AES, or headphone audio