Newsgroups: comp.speech
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From: viji@tifrvax.tifr.res.in
Subject: "Questions about audio input to Sun Sparc 10/51"
Message-ID: <13OCT94.05503217@tifrvax.tifr.res.in>
Sender: news@news.cern.ch (USENET News System)
Organization: Tata Institute of Fundamental Research
Date: Thu, 13 Oct 1994 05:50:32 GMT
Lines: 27

We have the following questions about Audio system associated with
Sun Sparc 10/51. Any help would be appreciated.

1) Even in the absence of any input, a strong noise with a 
 fundamental of about 67 Hz is present when the stereo-to-mono
 adapter supplied by Sun systems is connected to the audio pre-amplifier
 box (containing the speaker). The average amplitude of this
 noise component is about 500/32000 when digitized at 16 bit linear 
 mode; i.e., the maximum SNR of the recorded signal is about 35dB. Have 
 others observed this noise? Is there any way of obtaining better SNR?
 (The power supply line frequency is 50 Hz.)

2) When a microphone is connected to the stereo-to-mono adapter, 
 additional high frequency noise rides over the above mentioned 67 Hz 
 noise. We use Sennheisser made close-talking, noise-cancelling microphone
 headset (model HME 1410 KA). The microphone built-in pre-amplifier is 
 powered by a battery to avoid line interference. (The mic supplied by
 the Sun systems has poorer SNR.)

3) Due to combined amplification of the built-in pre-amplifier of the
 above microphone and the amplifier of the Sparc audio unit, even a normal 
 voice tend to saturate the amplifier even after reducing the 
 amplification of the Sparc amplifier to the minimum value (6 out of 
 100).

- Samudravijaya K
  chief@raman.csc.tifr.res.in
