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Path: utzoo!linus!philabs!cmcl2!seismo!umcp-cs!cvl!umd5!don
From: don@umd5.UUCP
Newsgroups: net.analog
Subject: Re:sound synthesizing(how to get sine from square)
Message-ID: <869@umd5.UUCP>
Date: Wed, 19-Feb-86 11:32:51 EST
Article-I.D.: umd5.869
Posted: Wed Feb 19 11:32:51 1986
Date-Received: Fri, 21-Feb-86 08:10:50 EST
References: <2930@wateng.UUCP> <818@kitty.UUCP>
Distribution: net.analog, net.micro
Organization: U of Md, CSC, College Park, Md
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> 	The only drawback is that the tone generators are all square wave.
> This may or may not be be a problem, depending upon your application.  If it
> is a problem, then you can use ONE chip per tone (i.e., only using one onchip
> tone generator), convert square wave to sine wave, and then sum the sine wave
> outputs.  In case you are not familiar with the process, there are many ways
> to convert a square wave to a sine wave - generally by integration to a
> triangular wave, which is then easily converted to a sine wave.
> 

Easier than that -- Just use a couple of notch filters at the square-wave's
fundamental. Or even a low-pass filter with Fc at the fundamental.
Whatever suits you. We (Apcom, Inc.) do this (notch filters) to obtain
a nice sine-wave high-speed tape recorder reference from TTL dividers
dividing the PLL crystal reference oscillator -- phase coherent recorder
reference with minimum pain.
Put the notch filter on a PCB, short tracks, plenty of ground plane.
You should have < 0.75% distortion easily (harmonics less than -46dBc).
Need less distortion ? Add another filter or two. Sure the filter are
lossy, but we follow the filter with a variable gain stage.

-- 
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