0dbfs — Sets the value of 0 decibels using full scale amplitude.
The default is 32767, so all existing orcs should work.
Amplitude values in Csound are always relative to a "0dbfs" value representing the peak available amplitude before clipping. In the original Csound, this value was always 32767, corresponding to the bipolar range of a 16bit soundfile or 16bit AD/DA codec. This remains the default peak amplitude for Csound, for backward compatibility. The 0dbfs value enables Csound to produce appropriately scaled values to whatever output format is being used, whether 16bit integer, 24bit integer, 32bit floats, or even 32bit integers.
OdBFS can be defined in the header, to set the amplitude reference Csound will use, but it can also be used as a varible inside instruments like this:
ipeak = 0dbfs
asig oscil 0dbfs, freq, 1 out asig * 0.3 * 0dbfs
The purpose of the 0dbfs opcode is for people to start to code 0dbfs-relatively (and use the ampdbfs() opcodes a lot more!), rather than use explicit sample values. Using 0dbfs=1 is in accordance to industry practice, as ranges from -1 to 1 are used in most commercial plugin formats and in most other synthesis systems like Pure Data.
Floats written to a file, when 0dbfs = 1, will in effect go through no range translation at all. So the numbers in the file are exactly what the orc says they are.
For more details on amplitude values in Csound, see the section Amplitude values in Csound
Here is an example of the 0dbfs opcode. It uses the file 0dbfs.csd.
Example 33. Example of the 0dbfs opcode.
See the sections Real-time Audio and Command Line Flags for more information on using command line flags.
<CsoundSynthesizer> <CsOptions> ; Select audio/midi flags here according to platform ; Audio out Audio in No messages -odac -iadc -d ;;;RT audio I/O ; For Non-realtime ouput leave only the line below: ; -o 0dbfs.wav -W ;;; for file output any platform </CsOptions> <CsInstruments> ; Initialize the global variables. sr = 44100 ksmps = 10 nchnls = 2 ; Set the 0dbfs to 1. 0dbfs = 1 instr 1 ; from linear amplitude (0-1 range) print p4 a1 oscil p4, 440, 1 outs a1, a1 endin instr 2 ; from linear amplitude (0-32767 range) iamp = p4 / 32767 print iamp a1 oscil iamp, 440, 1 outs a1, a1 endin instr 3 ; from dB FS iamp = ampdbfs(p4) print iamp a1 oscil iamp, 440, 1 outs a1, a1 endin </CsInstruments> <CsScore> ; Table #1, a sine wave. f 1 0 16384 10 1 i 1 0 1 1 i 1 + 1 0.5 i 1 + 1 0.1 s i 2 0 1 32767 i 2 + 1 [32767/2] i 2 + 1 [3276.7] s i 3 0 1 0 i 3 + 1 -6 i 3 + 1 -20 e </CsScore> </CsoundSynthesizer>