Conference napalm::commusic_v1

    I've heard that the earlier Mirages had a "problem" that was solved
    by the use of an outboard filter. Later models had the filter built
    in. The outboard unit sells for (I think) ~$150. This could affect
    your selling price, since you'd be within $50 of new. (I wish I'd
    remembered this earlier. Sorry)
    
    Which unit do you have?
    
    
    Edd

    
    I know the newer models have have improvents made, but I don't recall
    any "problems" I've had with it.  In fact, I've never heard of the
    outboard filter.  But maybe I've had my head in the sand too much
    lately.  I got it in Sept, so I believe it's one of the first models.
    
    	In any case, I'm still open for bids and negotiation.
    	(I kinda need the money)
    
    -Tom
    

    
    	Well I looked in the filter problem you mentioned.  Its an
    input filter that "smooths" out incoming samples that YOU create.
    That is, there's no difference in sound of the samples loaded from
    disk, but it cleans up any samples that do yourself.  You were right
    in price too, it sells for ~$150, and it does come with the new
    model.  So I guess I'll have to chop $150 off my selling price to
    make up for it, which would make it, (gulp) $1350.  But if I go
    any lower than that, I might as well keep it and buy the damn filter
    myself!  I guess that's what I get for being the first kid on the block
    with one !
    
    -Tom
    

    Sounds like the filter is an "anti-aliasing" filter.  "Aliasing"
    is what happens when your input contains frequencies higher than
    (half) the sampling rate.  You get a sort of "strobe" effect, as
    the sampling process captures pieces of these higher frequencies
    from later and later in their cycle, producing a spurious low frequency
    component (often at an obnoxious, inharmonic frequency) that isn't
    really there in the input but which shows up in the sample.
    
    BTW, it is the presence of anti-aliasing filters in the CD recording
    process (after all, it's just "sampling" a whole piece at a time)
    that offends the golden-ear audiophiles.  These filters usually have
    very steep cutoffs (so they don't affect the frequency balance in
    the audio band), butu as a consequence they have significant phase
    effects.  Most people believe that the ear can't hear all but the
    most eggregious phase effects, but anti-aliasing filters are not without
    side effects. 

    
    	Wow, is that all it is...?
    
    	And I thought it was something complicated...
    
    -Tom
    

    
    	Thanks for the added info, but I was just being sarcastic to
    the previous note, that's all.  It's interesting though...
    
    -Tom
    

    I can't believe that Ensoniq originally released a sampling machine with
    no front-end analog filter to clean up the signal!  That really
    makes me wonder about them as a company.  Isn't Ensoniq an off-shoot
    company founded by the guys that created the VLSI sound chip for the
    commodore-64?  As I recall, the mathematical formulas used for the filter
    specifications in this chip were all wrong (and still are).
    	Can't help but wonder about those Ensoniq engineers, but if
    it sounds fine and is a quality piece of gear, that's what counts.
    
    Todd
    

    Why did you feel it necessary or appropriate to be sarcastic to
    my explanation of what the filter was for?  I missed your sarcasm
    completely.  Next time I won't bother wasting anybody's time by
    explaining anything.
    
    len.
    

    Len,
    
                      WASTE MY TIME!!!
    
    I've got more out of you, Karl, Karl, John and the rest of the noters
    than I would from a ton of books! Nothing beats practical experience.
    
    I always wondered what anti-aliasing filters were/did. Now I know.
    No time wasted!
    
    Edd

    Well I for on was really pissed off and insulted that you would
    even venture to think you needed to explain what an anti-aliasing
    filter is.
    
    It's an option on the new Volvo Turbo isn't it?
    
    Dennis Savage

    
    	Whoa, didn't mean to cause an uproar.  I'm sorry if I offended
    anyone with my remark about the anit-aliasing filter.  It's just
    that I didn't expect such an in depth reply.  I mean, it was like
    saying my car doesn't have fuel injection and then having someone
    explain what fuel injection was.  Don't take it seriously, by all
    means Len, explain away !!
    
    -Tom
    

    Ok, no offense taken in retrospect.  Given your encouragement I'll
    take this opportunity to add one more remark, namely that there
    is also a filter necessary in the output side of any sampling
    device, which actually does "smoothe" the output, specifically
    remove the bogus high frequency information introduced by the "edges"
    of the "steps" generated by the D to A converters.  I originally
    posted the reply about anti-aliasing filters because I thought
    (presumptuous of me, I admit) you (or someone else) might be confusing
    the roles of the input and output filters.

    len (who has a compulsive need to explain)
    

    
    	To tell you the truth I didn't really comprehend your explanation
      at first, not because it wasn't a good explanation, but because
      I'm not really into sampling yet.  But I was just reading my
      friend's Advanced Samplers Guide for the Mirage, and now I understand
      it.  Someone made a remark earlier in this note about learning
      more from you and others in these notes than in a ton of books.
      I'm starting to see why...
    
    -Tom (who has a need to be sarcastic)
    
    

    Tom, is your Mirage still for sale?
    
    Is your friend's Mirage still for sale?
    
    Sorry if this is a little late (only about a year!), but I just
    started here (DEC) in February (1987) and just saw your note now!
    
    Mike D.