The Nominal Level represents the optimal operating level of a signal in audio systems or equipment. This value indicates at what level the signal should be appropriately processed or operated. The Nominal Level is a critical concept for maintaining compatibility and consistency between different devices and components. It is established by taking various factors such as Noise Floor, Dynamic Range, and Clipping into consideration.
[Is the Nominal Level the same as the Reference Level?]
Not necessarily. The Nominal Level represents the actual operating level of the equipment, which can differ from internationally standardized line levels. For example, international standards like AES/EBU and SMPTE set the line level standard at +4dBu, but the actual Nominal Level of a piece of equipment could differ from this. If the Nominal Level of a device is +4dBu, that means it is built to standard specifications. If that device also processes digital signals, its Nominal Level will be aligned with the digital reference level. For instance, +4dBu in analog signals corresponds to -18dBFS in digital signals.
Link to Reference Level document
Conversely, if the Nominal Level is -2.5dBu, that piece of equipment is designed to operate at -2.5dBu, making it non-standard compared to the +4dBu standard. The same applies to digital equipment; non-standard devices may have a different Nominal Level. For example, standard digital equipment should match +4dBu with -18dBFS, therefore offering 18dB of headroom. (AES/EBU: -18dBFS, SMPTE: -20dBFS)
In the case of analog equipment, the Nominal Level is generally +4dBu, while consumer-level equipment is made at -10dBV. Digital equipment is usually designed around +4dBu or a corresponding digital reference level, and the maximum input/output levels are set accordingly. For this reason, when connecting analog and digital equipment, it’s often necessary to use the Trim function to adjust each device’s levels.
Reference equipment refers to devices designed based on international standards. These devices usually have a Nominal Level of +4dBu and maximum input/output levels of 22dBu or 24dBu as per SMPTE or EBU standards. Such reference equipment often includes high-quality A/D and D/A converters and offers a variety of configurable input/output levels for compatibility.