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Article #2432Re: DSP for audio work
From: robert bristow-johnson
Date: Mon, 25 Mar 2002 20:10
Date: Mon, 25 Mar 2002 20:10
40 lines
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3028 bytes
In article 3C9F7941.28284E08@bittware.com, Jim Thomas at jthomas@bittware.com wrote on 03/25/2002 14:23: > robert bristow-johnson wrote: >> >> In article 3c9f0b75.31395314@news.optusnet.com.au, Johnny at >>> I also Think that 24bit is plenty good enough for audio. But 32bit >>> bit floating point is a lot like 24bit fixed point with an 8-bit >>> exponent term. >> >> well, it's *exactly* like a 25 bit fixed-point (there's a "hidden 1 bit") >> with an 8 bit exponent. > > Don't forget about the sign bit. There are only 23 bits of mantissa, so > the hidden bit makes the 24th. yeah, but if you're comparing apples to apples, the 24 bit fixed-point PCM word has the sign bit as part of the word (with 23 other bits). so with regular, vanilla-flavored floating point, there is the sign bit + 24 "other bits", making it 25. how else can we look at it?: 32 bit float, subtract 8 bit exponent leaving 24 bits, add "hidden 1 bit" and you've got 25. for a signal that peaks at + or - 1 (or just a hair below like + or - 0.999999), the exponent gets as large -1 (represented as 126) and no larger and your largest quantization error is -150 dB below that, not -144 as would be the case with a 24 bit fixed-point value. isn't that right, Jim, or did i screw up? -- r b-j Wave Mechanics, Inc. 45 Kilburn St. Burlington VT 05401-4750 tel: 802/951-9700 ext. 207 http://www.wavemechanics.com/ fax: 802/951-9799 robert@wavemechanics.com --
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X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: 112d1e,d43e8f202cc9402f X-Google-Attributes: gid112d1e,public X-Google-Thread: 103407,d43e8f202cc9402f X-Google-Attributes: gid103407,public X-Google-Thread: f8fcc,ad386b215662caf0 X-Google-Attributes: gidf8fcc,public X-Google-ArrivalTime: 2002-03-25 12:10:55 PST Path: arc1-ca.pugleaf.net!archiver1.google.com!news1.google.com!newsfeed.stanford.edu!news-spur1.maxwell.syr.edu!news.maxwell.syr.edu!newsfeed1.cidera.com!Cidera!cyclone1.gnilink.net!spamfinder.gnilink.net!nwrddc02.gnilink.net.POSTED!53ab2750!not-for-mail User-Agent: Microsoft Outlook Express Macintosh Edition - 5.01 (1630) Subject: Re: DSP for audio work From: robert bristow-johnson <robert@wavemechanics.com> Newsgroups: sci.electronics.design,aus.electronics,comp.dsp Message-ID: <B8C4EE7E.33B3%robert@wavemechanics.com> References: <3c9da171.2670537@news.optusnet.com.au> <3c9db1ea.6888487@news.optusnet.com.au> <Xns91DB81B2F6D2aclarkdanvillesignal@209.249.90.101> <71f9eeeb.0203242213.38c15576@posting.google.com><3c9f0b75.31395314@news.optusnet.com.au> <B8C4B37E.3336%robert@wavemechanics.com><3C9F7941.28284E08@bittware.com> Mime-version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-transfer-encoding: 7bit Lines: 41 Date: Mon, 25 Mar 2002 20:10:55 GMT NNTP-Posting-Host: 64.222.82.246 X-Complaints-To: abuse@verizon.net X-Trace: nwrddc02.gnilink.net 1017087055 64.222.82.246 (Mon, 25 Mar 2002 15:10:55 EST) NNTP-Posting-Date: Mon, 25 Mar 2002 15:10:55 EST