Microphone Gain Control; Speech Processors - Kenwood TS-990S In-Depth Manual

Microphone Gain Control

The microphone gain is digitally adjusted by rotating the [MIC] knob (on the front panel).
Audio from the microphone is converted by the A/D converter to a digital signal and is then sent to the DSP. The TX
audio signal entered into the DSP is subject to the band limitation by the TX filter, and its level is adjusted by the AF
AGC so as not to exceed the reference level configured for the DSP. If the signal level exceeds the reference level, for
instance, when the configured value of the microphone gain is higher than the audio signal level for transmission, the
audio gain level for transmission will be lowered. The reference level is equivalent to the level that fully deflects the ALC
meter needle for SSB mode and to the maximum factor of modulation for AM and FM modes.
The TS‑990S allows the modulation of multiple signals that are combined with the input signal from the ACC 2 connector, the
signal from USB audio input and optical digital input as well as that from the microphone (either the ACC 2 connector input
or USB audio input is exclusively selectable). The microphone gain on the respective paths can be independently adjusted.
As described as above, you can configure the microphone gain by rotating the [MIC] knob, and the gains for other sound
sources are configured in the Menu screen. The microphone gains are adjusted by path, and the signals from the respective
path are mixed and sent to the TX filter. Consequently, the TX audio gain control is applied to a mixed audio signal.
Fig. 76 Microphone, ACC2 Connector, USB Audio Input, Optical Digital Input, and Gain Processing

Speech Processors

The TS‑990S employs a speech processor placed in the IF stage for SSB mode (hereinafter referred to as the IF speech
processor) and a speech processor in the AF stage for AM and FM modes (hereinafter referred to as the AF speech processor).
The speech processor amplifies the average power for the entered audio from the microphone within the limit of the
maximum power to enhance the intelligibility of the receiving stations. The speech processor amplifies the average
power as a function intended for SSB mode, in addition the speech processor can increase the average modulation in
AM and FM modes, enhancing the intelligibility of the receiving station.
The IF speech processor compresses the modulated wave in the IF stage. Unlike the compression in the AF stage,
harmonics generated by distortion due to compression are outside the audio band. From the compressed signal, the
bandpass filter eliminates distortion components outside the audio band, thus it implements a high average power (talk
power) with less distortion than that of the AF speech processor.
To pursue an emphatic sound to be called back during pileup, select "Hard" from the Speech Processor Effect screen.
In comparison with "Soft", this causes more compression of the modulated wave. The TS‑990S is designed not to differ
the frequency characteristics even if the Speech Processor Effect is toggled between "Hard" and "Soft".
By monitoring the transmitting audio signal and viewing the COMP meter deflection, you can rotate the [PROC IN] knob
until the compression level is adjusted as appropriate, and by viewing the ALC meter deflection, you can rotate the
[PROC OUT] knob until the level is adjusted as appropriate.
The graphs below show modulated signal waveforms while the IF speech processor is inactive and if waveforms of
modulated signals which are compressed respectively with "Soft" configured or with "Hard" configured.
DSP 06
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