DbToAmp.csd Written by Iain McCurdy, 2008 -odac -dm0 sr = 44100 ksmps = 8 nchnls = 2 0dbfs = 1 ;MAXIMUM AMPLITUDE VALUE USED BY CSOUND WILL BE '1' ;FLTK INTERFACE CODE;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; FLcolor 255, 255, 255, 0, 0, 0 FLpanel "Convert decibels to amplitude", 500, 120, 0, 0 ;VALUE DISPLAY BOXES WIDTH | HEIGHT | X | Y iddb FLvalue " ", 100, 18, 5, 45 idamp FLvalue " ", 100, 18, 5, 95 ;SLIDERS MIN | MAX | EXP | TYPE | DISP | WIDTH | HEIGHT | X | Y gkdb, gihdb FLslider "Decibels", -90, 0, 0, 23, iddb, 490, 25, 5, 20 gkamp, gihamp FLslider "Amplitude", 0, 1, 0, 23, idamp, 490, 25, 5, 70 ;SET INITIAL VALUES FOR SLIDERS FLsetVal_i -90, gihdb FLsetVal_i 0, gihamp FLpanel_end ;INSTRUCTIONS AND INFO PANEL FLpanel " ", 500, 600, 512, 0 ;TEXT BOXES TYPE | FONT | SIZE | WIDTH | HEIGHT | X | Y ih FLbox " convert decibels to amplitude values ", 1, 5, 14, 490, 15, 5, 0 ih FLbox "-------------------------------------------------------------", 1, 5, 14, 490, 15, 5, 20 ih FLbox "This example converts between amplitude and decibel (db) ", 1, 5, 14, 490, 15, 5, 40 ih FLbox "and allows the user to observe the relationship by ", 1, 5, 14, 490, 15, 5, 60 ih FLbox "synchronising the two sliders. Either slider can be moved and", 1, 5, 14, 490, 15, 5, 80 ih FLbox "the other will move in sympathy. ", 1, 5, 14, 490, 15, 5, 100 ih FLbox "A positive value measurement of decibels is really only ", 1, 5, 14, 490, 15, 5, 120 ih FLbox "relevant if we are measuring the level of the sound emanating", 1, 5, 14, 490, 15, 5, 140 ih FLbox "from the loudspeakers and this is dependent upon the setting ", 1, 5, 14, 490, 15, 5, 160 ih FLbox "made on the amplifier - a value Csound is unaware of. For ", 1, 5, 14, 490, 15, 5, 180 ih FLbox "this reason it is common to adopt the convention of defining ", 1, 5, 14, 490, 15, 5, 200 ih FLbox "decibels within Csound as negative value below 0db, 0db ", 1, 5, 14, 490, 15, 5, 220 ih FLbox "representing maximum amplitude (or unaltered amplitude in the", 1, 5, 14, 490, 15, 5, 240 ih FLbox "case of the playback of sound files). We cannot really ", 1, 5, 14, 490, 15, 5, 260 ih FLbox "achieve zero amplitude by reducing the decibels value as all ", 1, 5, 14, 490, 15, 5, 280 ih FLbox "we are dioing is reducing amplitude exponentially smaller and", 1, 5, 14, 490, 15, 5, 300 ih FLbox "smaller. In practice, perceived silence is achieved somewhere", 1, 5, 14, 490, 15, 5, 320 ih FLbox "between -70 and -100 db depending on how loud the speakers ", 1, 5, 14, 490, 15, 5, 340 ih FLbox "are. ", 1, 5, 14, 490, 15, 5, 360 ih FLbox "To convert decibels to amplitude we are using the 'ampdbfs' ", 1, 5, 14, 490, 15, 5, 380 ih FLbox "opcode ('fs' stands for full scale) and to convert from ", 1, 5, 14, 490, 15, 5, 400 ih FLbox "amplitude to decibels we are using 'dbfsamp'. ", 1, 5, 14, 490, 15, 5, 420 ih FLbox "By using the 'full scale' reference we can alter the value ", 1, 5, 14, 490, 15, 5, 440 ih FLbox "Csound uses for its full scale amplitude using the '0dbfs' ", 1, 5, 14, 490, 15, 5, 460 ih FLbox "opcode from the default 32768 to anything else (probably '1')", 1, 5, 14, 490, 15, 5, 480 ih FLbox "and Csound will still convert between amplitude and decibels ", 1, 5, 14, 490, 15, 5, 500 ih FLbox "appropriately. It is becoming the convention to set 0db to ", 1, 5, 14, 490, 15, 5, 520 ih FLbox "'1' when using Csound so it is advisable to use this method. ", 1, 5, 14, 490, 15, 5, 540 ih FLbox "This example uses this amplitude/decibel setting to scale the", 1, 5, 14, 490, 15, 5, 560 ih FLbox "playback amplitude of a sound file. ", 1, 5, 14, 490, 15, 5, 580 FLpanel_end FLrun instr 1 kdbold init -90 ;INITIALISE OLD VALUE FOR DECIBELS FOR FIRST PASS kampold init i(gkamp) ;INITIALISE OLD VALUE OF AMPLITUDE FOR FIRST PASS if kdbold!=gkdb then ;IF OLD VALUE FOR DECIBELS IS NOT THE SAME AS THE NEW VALUE... gkamp = ampdbfs(gkdb) ;...DERIVE A NEW VALUE FOR AMPLITUDE AS FROM NEW VALUE FOR DECIBELS FLsetVal 1,gkamp,gihamp ;SET AMPLITUDE SLIDER BASED ON DECIBELS NEW VALUE elseif kampold!=gkamp then ;IF OLD VALUE FOR AMPLITUDE IS NOT THE SAME AS THE NEW VALUE... gkdb = dbfsamp(gkamp) ;...DERIVE A NEW VALUE FOR DECIBELS FROM NEW VALUE FOR AMPLITUDE FLsetVal 1,gkdb,gihdb ;SET DECIBELS SLIDER BASED ON THE NEW VALUE FOR AMPLITUDE endif kdbold = gkdb ;SET DECIBELS 'OLD VALUE' FOR NEXT PASS kampold = gkamp ;SET AMPLITUDE 'OLD VALUE' FOR NEXT PASS aL,aR diskin2 "Songpan.wav",1,0,1 ;READ A SOUND FILE FROM DISK outs aL*gkamp, aR*gkamp ;SEND READ AUDIO TO OUTPUTS AND SCALE USING AMPLITUDE (OR DECIBELS VIA CONVERSION) VALUE endin i 1 0 3600 ;INSTRUMENT 1 PLAYS FOR 1 HOUR