AD8111_audio signal support

Document created by analog-archivist Employee on Feb 23, 2016
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One customer asked whether AD8111 can support audio signal? In AD8113
datasheet, it specifies very clearly that it can support audio signal. The
difference is that AD8113 can support +/-12V power supply if it is for audio
signal switching.  How about AD8111?


It might be possible for the AD8111 to support audio signals, but it probably
won't be optimum. The major issue with audio signals is that there is not a
defined upper limit on the amplitude.
Unlike video signals, which have a defined maximum amplitude--usually 700 mV or
1V---, audio signals do not have such definition. Part of this issue is a
result of the fact that the dynamic range of human hearing is greater than the
visual range.
Thus, if you use the AD8111 for audio signals there will be limited dynamic
range. It is possible to attenuate the entire audio signal to try to get it to
"fit" into the AD8111 dynamic range, but there will come a point when noise
issues will diminish the signal quality.
In fact, we specifically designed the AD8113 with high dynamic range
specifically because we got so many requests for it from out video customers
who also wanted to route audio. ADI has many other audio groups, and we are
basically a video group. But since we had the crosspoint knowledge, we did this
as basically our only audio part.
Why does the customer want to use the AD8111? Is it because it is 16 x 8. If
that's what the customer needs, he can use the AD8112 which is a 16 x 8 version
of the AD8113 (same die actually). 
Overall, if not much dynamic range is required, and the audio quality is not
too important, then the AD8111 will probably work. But if you want better audio
performance in a 16 x 8 crosspoint, then the AD8112 will work better.
I even see that on the ADI product selection page, the listed price for the '12
is much lower than the '11.  A part of the reason for this kind of pricing is
that higher-bandwidth video applications will pay more for functions than audio
applications. We try to charge the price that customers are willing to pay.