[TUHS] Bell-Era UNIX Audio/DSP Interfaces?

[Kevin Bowling]

On Mon, Jan 6, 2025 at 2:21 PM segaloco via TUHS <tuhs at tuhs.org> wrote:
>
> The sound situation in the UNIX world to me has always felt particularly
> fragmentary, with OSS offering some glimmer of hope but faltering under the long
> shadow of ALSA, with a hodge podge of PCM and other low level interfaces
> littered about other offerings.
>
> Given AT&T's involvement with the development of just about everything
> "sound over wires" for decades by the time UNIX comes along, one would suspect
> AT&T would be quite invested in standardizing interfaces for computers
> interacting with audio signals on copper wire.  Indeed much of the ESS R&D was
> taking in analog telephone signals, digitizing them, and then acting on those
> digitized results before converting back to analog to send to the other end.
>
> Where this has me curious is if there were any efforts in Bell Labs, prior to
> other industry players having their hands on the steering wheel, to establish an
> abstract UNIX interface pattern for interacting with streams of converted audio
> signal.  Of course modern formats didn't exist, but the general idea of PCM was
> well established, concepts like sampling rates, bit depths, etc. could be used
> in calculations to interpret and manipulate digitized audio streams.
>
> Any recollections?  Was the landscape of signal processing solutions just so
> particular that trying to create a centralized interface didn't make sense at
> the time?  Or was it a simple matter of priorities, with things like language
> development and system design taking center stage, leaving a dearth of resources
> to direct towards these sorts of matters?  Was there ever a chance of seeing,
> say, the 5ESS handling of PCM, extended out to non-switching applications, or
> was that stuff firmly siloed over in the switching groups, having no influence
> on signal processing outside?

You might be synthesizing a bit of serendipity that wasn't there in
the moment in both directions: what switches were and where multimedia
wasn't yet.  The 5ESS is primarily concerned with time/space/time
switching, that those slots are PCM audio, signalling, or data is not
so important beyond getting it to the right place on time.  To
potentially highlight the distinction, you need a seperate machine
(potentially many) called an announcement system, to produce what
you'd assume to be intrinsic and familiar audio necessary for end user
telephony on a 5E.  So it is not so great at much related to computer
audio unless you consider line interface units really expensive
ADC/DAC.  And that is the domain of microcontrollers far away from
UNIX.  It might live on completely separate machines like channel
banks or SLC systems.  So the BORSCHT part of getting analog audio in
and out predates all this and maybe PCM _is_ the great achievement for
computer audio, because regardless of how the audio is produced or
encoded it probably lives as PCM at your DAC.

I will speculate that the AT&T folks didn't yet have pressing need for
UNIX to have rich multimedia capabilities so they just weren't in the
position to define lasting APIs - you can find historical research
systems of the IBM mainframe and DEC variety where people were
figuring out things like music and speech synthesis at Bell and
elsewhere.  But for Big Telecom, think more like TI's Speak&Spell...
microcontroller, PCM ROM, DAC..  That's the way electronic phone
systems were designed when it came time to produce audio, as
distributed systems of microcontrollers or DSPs and fixed function
ASICs, with as little involvement from anything resembling a full OS
as possible.  It wasn't until the 1990s that Computer Telephony (CT)
really took off, with vendors like Dialogic, or later on software like
Asterisk.  That was maybe concurrent to the Multimedia PC of the early
1990s where the desire went beyond games synthesis or commanding a
CD/LaserDisc's PCM to storing, processing, and playback of media files
-- now you need audio APIs -- and AT&T is no longer in the driver's
seat.  OSS is pretty good, and was in there by the time Univel took
the helm of UNIX where they thought so too so it might be as close to
official as one can get.  Audio is one of those areas where Linux
earns the facepalm.

Cheers,

> - Matt G.