For the purposes of the present document the terms narrowband, wideband, super-wideband and fullband refer to signals associated with the corresponding operating modes of the speech codecs specified in TS 26.132. For the purposes of the present document, the terms dB, dBr, dBm0, dBm0p and dBA, shall be interpreted as defined in ITU-T Recommendation B.12 [2]; the term dBPa shall be interpreted as the sound pressure level relative to 1 pascal expressed in dB (0 dBPa is equivalent to 94 dB SPL). The overload point (maximum load capacity) is for the purposes of this document defined as the RMS level of a digital representation of a full-scale pure tone at the input of the speech encoder. The overload point is defined at 3,14 dBm0 for AMR, AMR-WB and EVS speech codecs. A 3GPP softphone is a telephony system running on a general purpose computer or PDA complying with the 3GPP terminal acoustic requirements (TS 26.131 and TS 26.132). For the purposes of the present document the term clock skew is defined as the difference between the clock of the device under test (C_DUT) and the clock of the reference client (C_REF). The skew of C_DUT relative to C_REF is defined in parts per million (PPM) as: (C_DUT -C_REF).10⁶/ C_REF. For the purposes of the present document, the term electrical interface is defined as an analogue or digital access to a UE, which allows injecting and capturing signals electrically instead of through an acoustical interface. The interface can be either analogue (wired) or digital (wired or wireless). The purpose of this interface is to connect a separate device (typically a headset), which provides a receiver and transmitter for telephony.

For the purposes of the present document, the following abbreviations apply: ADC AMR DAC DAI DRP DTX EEC EL ERP EVS HATS G-MOS-LQOn G-MOS-LQOw G-MOS-LQOfb IMS LSTR LTE MRP MTSI OLR N-MOS-LQOn N-MOS-LQOw N-MOS-LQOfb NR PCM PDA POI PSTN RLR S-MOS-LQOn S-MOS-LQOw S-MOS-LQOfb SLR STMR SS TX UE UMTS UPCMI WLAN

The interfaces required to define terminal electro-acoustic characteristics are shown in TS 26.132. These are the air interface and the point of interconnect (POI). The interfaces are shown for one-channel (mono) operation, interfaces for two-channel (stereo) operation are for further study. Measurements can be made using the system simulator (SS) described in TS 26.132. MTSI speech aspects are specified by TS 26.114.

The Air Interfaces for GSM, 3G, LTE and NR are specified by GSM 05, 3GPP 45, 3GPP 25, 3GPP 36 and 3GPP 38 series specifications, and the Air Interface for WLAN access to EPC is specified by WLAN access to EPC as defined in TS 23.402 and TS 24.302. The POI with the public switched telephone network (PSTN) is considered to have a relative level of 0 dBr.

The following classes of acoustical interface are considered in this specification:

• Handset UE including softphone UE used as a handset;
• Headset UE including softphone UE used with headset;
• Desktop-mounted hands-free UE including softphone UE with external loudspeaker(s) used in hands-free mode;
• Hand-held hands-free UE including softphone UE with internal loudspeaker(s) used in hands-free mode.

(See definition of softphone in Clause 3.1) Vehicle Mounted Hands-free UE is out of scope. In case performance evaluations are planned for Vehicle Mounted Hands-free UE, test setup, methods and requirements specified in Recommendation ITU-T P.1100 [21] (for NB), P.1110 [22] (for WB) or P.1120 [23] (for SWB and FB) can be used. The requirements and performance objectives for a softphone UE shall be derived according to the following rules:

• When using a softphone UE as a handset: requirements and performance objectives shall correspond to handset mode.
• When using a softphone UE with headset: requirements and performance objectives shall correspond to headset mode.
• When using a softphone UE in hands-free mode:
  • When using internal loudspeaker(s), requirements and performance objectives shall correspond to hand-held hands-free.
  • When using external loudspeaker(s), requirements and performance objectives shall correspond to desktop-mounted hands-free.

An electrical interface is considered in this specification and details on standardized analogue (wired) and digital (wired and wireless) headset interfaces can be found in TS 26.132. For the electrical interface, the POI in sending / receiving direction is respectively defined as the input / output of the reference speech coder of the system simulator. Any of the UE types mentioned in clause 4.3 providing an electrical interface can be considered as Electrical Interface UE.