Sound chip for the Personal IRIS
Sanjay Iyer
sanjay at nirvana.esd.sgi.com
Thu Sep 7 09:32:18 AEST 1989
In article <8908311403.AA05313 at zorac.DCIEM.DND.CA>, tim at zorac.dciem.dnd.ca (Tim Pointing) writes:
> > The sound chip exists on all Personal Irises. The only documentation is
> > the man page for the driver /dev/audio. You will need to get a speaker
> > and microphone. The PI has miniature audio jacks in the back.
>
> Does anybody have any info on things like leves and impedences for these
> jacks or are they some "standard"?
This ought to help:
PERSONAL IRIS AUDIO I/O INFORMATION
Line input:
+/- 2.5 v (input is AC coupled) is full scale to ADC
ADC is 8-bit, 2's complement
Input impedance is 22K ohms.
Input gains not adjustable.
Frequency response:
20 Hz - 13 KHz @ 32K/sec sampling rate
20 Hz - 6.6 KHz @ 16K/sec sampling rate
20 Hz - 3.3 KHz @ 8K/sec sampling rate
Microphone input:
+/- 3.8 mv (input is AC coupled) is full scale to ADC
ADC is 8-bit, 2's complement
Input impedance 330 ohms.
Designed for use with 300 ohm microphone.
Input is summed (analog) with line input.
Output:
With full output gain (0xff) and no load, output swings +/- 4.9 v.
Reduced output gain linearly reduces swing.
Output is AC coupled (~4 ohms in series with 220 uf).
Can directly drive 8 ohm speaker.
(By the way there is no single sound chip; the audio circuit is composed of
a combined ADC-DAC, another DAC for output gain control, a switched-capacitor
filter, and misc amps).
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