This repository contains some explanations and functionalities to calibrate digital to analog reference levels using EBU R68 or SMPT RP155 [1] standard and Dolby calibration used in K-System [2, 3], which map -20dBFS(RMS) to 0VU or +4dBu in professional equipment.
This repository provides a way to map digital to analog level scaling (dBFS to dBu). It might be useful to sample audio gear (referenced to voltage or dBu) using a soundcard with digital level scaling (dBFS). Also it provides some functionalities to understand the level conversion and references between dBFS and dBu units using different standards (EBU R68, SMPTE RP155 or a customized one).
Currently the soundcard's manufacturer don't use EBU R68 or SMPTE RP155 standards. However they always provide a MAXIMUM OUTPUT LEVEL in dBu that we can use to map signals from a dBFS scale.
Here a list with different customized output level standards in different soundcards:
| Manufacturer | Model | Maximum Output Level |
|---|---|---|
| Focusrite | Scarlet 2i2 | +10dBu |
| RME | UC - Fireface 400 | +2dBV, +13dBu and +19dBu |
| UA | Apollo Twin MKII | +20.2dBu |
| Audient | id4 | +12dBu |
| Avid | HD I/O | +22dBu |
The table below shows only AVID HD I/O is following the SMPTE RP155 standard. It is clear the rest of manufacturers are applying customized standards that can generate differences in voltage levels if you reproduce the same signal with different soundcard.
When we want to sample audio gear with a correlated scaling we should bear in mind the specifications provided by the manufacturer and apply the maximum output level to the converters of this repository.
Obviously it is different to sample a processor prepared for TRS cable (balanced signals) than an instrument like a synthesizer which are prepared for TS cables (unbalanced signals). Using TS cables will provide -6dB of the maximum output level.
The requirements.txt file contains the Python modules necessary for this project. We suggest to create a virtual environment to have a clean installation.
To build a virtual environment, you might use venv,
python3 -m venv envFor installing packages in the virtual environment:
- Activate your
env:
source env/bin/activate- Install Python packages:
pip install -r requirements.txtHere some examples to display the level table, which maps dBFS -> dBu -> Volts
src/level_list.py generates a list/table to display the level mapping between dBFS, dBu and Volts.
python level_list.py
>>> SMPTE_RP155
dBFS dBu Volts
0 0 24 12.283
1 -1 23 10.947
2 -2 22 9.757
3 -3 21 8.696
4 -4 20 7.750
5 -5 19 6.907
6 -6 18 6.156
...You can also specify the bottom level and the standard to use (SMPTE RP155 by default):
python level_list.py -b -58 -s ebu_r6Sometimes, we also need to have some reference between the different scalings: dBFs-> dBu, Vpeak -> Vrms (for sinusoidal signal)
python dbfs_to_volts.py -20
>>> -20.0 dBFS -> 4.0 dBu -> 1.228 V
>>> 1.228 Vpeak -> 0.869 Vrmsor Volts to dBFS using -i flag
python dbfs_to_volts.py 1.2283 -i
>>> 1.228 V -> 4.0 dBu -> -20.0 dBFSpython peak_to_rms.py 1.228
>>> 1.228 Vpeak -> 0.868 Vrmsor RMS to peak-to-peak:
python peak_to_rms.py 0.868 -i
>>> 0.868 Vrms -> 1.228 Vpeak"RP 155:2014 - SMPTE Recommended Practice - Reference Levels for Analog and Digital Audio Systems," in RP 155:2014 , vol., no., pp.1-7, 29 Dec. 2014, doi: 10.5594/SMPTE.RP155.2014.
Katz, B. (2000). Integrated approach to metering, monitoring, and leveling practices, part 1: Two-channel metering. Journal of the Audio Engineering Society, 48(9), 800-809.
Katz, B., & Katz, R. A. (2003). Mastering audio: the art and the science. Butterworth-Heinemann.
Brixen, E. B. (2020). Audio Metering: Measurements, Standards, and Practice. Focal Press.