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computers and DSP



> I am trying to make a decision to stay PC or convert to MAC.

Computer engineering is complicated!  I'm working on a paper that 
analyses the audio performance of the various processor options on the 
market.  I will let this community know when it is available for public 
consumption, but in the meantime here are a few ideas for you to 
consider.

The wintel chips are currently available with higher clock speeds, 
which means they can execute more instructions per second.  However, 
the motorola chips in the Mac benefit from a greater emphasis on 
pipelining/parallel execution, which means they can compute more 
processes simultaneously.  Some audio algorithms (like FFTs) can take 
advantage of parallel processing and some (like recursive filters) 
cannot.  Therefore there really is no "best" computer for audio.  It 
totally depends on what algorithms you are going to use.

One thing that is often overlooked by people evaluating computers is 
memory cache.  When you're doing audio processing the computer spends a 
lot of time shuffling memory between the processor and your RAM.  In a 
lot of situations this is the bottleneck - your processor actually sits 
there and does nothing for a large percentage of the time while it 
waits for the information it needs to arrive from the bus.  Cache keeps 
recently-used and maybe-soon-to-be-used data close to the processor to 
minimize this waiting.  The more cache you have, the more data you can 
keep close to the processor.

There is a painful real-world example of the effect of this phenomenon: 
when Apple upgraded their powerbook line from the G4 400/500 to G4 
550/667, for some reason they decided to change from 1MB of slower, 
off-chip cache to 256k of faster, on-chip cache.  The result is that 
despite the increased clock rate of the new computers, audio 
performance in many areas took a big hit.  A very unscientific test is 
documented at XLR8yourmac 
(http://xlr8yourmac.com/archives/jun02/060302.html): the maximum number 
of logic audio platinumverbs simultaneously runnable on the 500 was 13; 
for the 550, it dropped to 7; for the 667 only 9!!  Subsequent 
generations of G4 laptops have their big 1MB cache back.  It is worth 
noting that most wintel chips have only 256k of cache.

Also, it's super important to keep in mind that there are many 
considerations aside from the processor that will affect your work in 
audio, some of which are arguably much more important!  These include 
budget, efficiency and familiarity with the operating system associated 
with the chip, availability of software, hard drive size and speed, 
upgrade potential, bus speed, effective memory bandwidth, the ethics of 
the software company in control of the platform...

good luck.
Ben

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