May 2009 - chuck-users - lists.cs.princeton.edu

Re: [chuck-users] dbtopow(), dbtorms(), powtodb(), powtorms() off by 100 db (Robert Poor)
by Perry R Cook 03 May '09

03 May '09

dB just implies 20log_10. A reference must be selected. The most common are dBV (1 volt = 0dB), dBm (0dB = 1 milliwatt into 600 ohms), and dBSPL (watts relative to threshold of hearing at 0dB). I suspect that the implementers of this were thinking about the approximate 96dB of 16 bit audio, and the +/-1.0 float recommended max range of STK. Thus a range of 0.00001=0dB to 1.0=100dB resulted. Easy to change to any reference by just subtracting/adding/multiplying/dividing by a constant. PRC

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dbtopow(), dbtorms(), powtodb(), powtorms() off by 100 db
by Robert Poor 03 May '09

03 May '09

In chuck 1.2.1.2, the family of db conversion functions appear to be broken, or at least have a unconventional interpretation of db -- they all seem have an offset of 100 db: for example: Std.powtodb(1.0) => 100.0 (expected 0.0) Std.powtodb(10.0) => 110.0 (expected 10.0) Std.dbtopow(0) => 0 (expected 1.0) Std.dbtopow(100) => 1.0 (expected 10000000000) (Similar comments apply to rmstodb() and dbtorms()) OTOH they are self-consistent, in that Std.dbtopow(Std.powtodb(x)) == x, so maybe someone thinks that's how they're supposed to behave? - Rob

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Useful code snippet: writing to mono or stereo files
by Robert Poor 03 May '09

03 May '09

Thanks to a tip from Tom Lieber (who pointed out that WvOut doesn't actually handle stereo files), here's a snippet of ChucK code people might find useful: if (me.args() > 1) { dac.chan(0) => Gain g0 => WvOut w0 => blackhole; dac.chan(1) => Gain g1 => WvOut w1 => blackhole; 0.5 => g0.gain; 0.5 => g1.gain; me.arg(0) => w0.wavFilename; me.arg(1) => w1.wavFilename; <<< "writing stereo output to files", me.arg(0), me.arg(1) >>>; } else if (me.args() > 0) { dac => Gain g => WvOut w => blackhole; 0.5 => g.gain; me.arg(0) => w.wavFilename; <<< "writing mono output to file", me.arg(0) >>>; } Since it attaches to the dac, you can put it just about anywhere in your ChucK program. When you invoke chuck as in : % chuck mytest.ck:bleeep.wav it will write everything your program sends to the dac to a mono "bleeep.wav" file. If you invoke it as in: % chuck mytest.ck:bleep_0.wav:bleep_1.wav it will write everything you program sends to the dac to two mono files: bleep_0.wav (left channel) andn bleep_1.wav (right channel). It's up to you to weave the two files together into a stereo sound file. There are several ways to do it -- I tend to use Audacity. - Rob

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