HD+ Voice: calls clearer than VoLTE

What "HD+" means

How natural a voice sounds depends on how much of it a call carries. A normal 2G/3G phone call carries roughly 300 Hz to 3.4 kHz. A VoLTE "HD Voice" call (the AMR-WB codec) goes to about 7 kHz; some newer networks with the EVS codec go further. Muslim Chat sends Opus, mono, at 48 kHz — the full band, 20 Hz to 20 kHz — so consonants like "s" and "f" stay crisp and voices are easy to tell apart. Direct calls use 32 kbps with 20 ms packets; calls carried by the Muslim Chat server, including group calls, use 24 kbps.

Clear even on a weak network

Voice packets also carry a copy of the previous one (redundancy and forward error correction), so when the network loses a packet the app rebuilds it instead of letting you hear a crackle. Every few seconds the call checks how the line is doing: it steps the bitrate down when packets are lost or the round trip is slow, and climbs back up when the line is clean.

Some networks — offices, hotels, certain mobile operators — block direct connections between phones. When that happens, Muslim Chat sends the call's audio through its own server, so the call still connects.

Data use

Because an HD+ call carries the full band and a repair copy of each packet, it uses more data than a basic call. Turn on Use less data for calls in Settings → Storage and data and calls use about half the data — still clear for talking. Group calls never send silence, so only the people talking use upload data.

Do I need VoLTE?

No. VoLTE is a feature of your mobile operator and your phone. Muslim Chat calls go over the internet, so they work on any Wi-Fi or mobile data connection — in Bangladesh or abroad — without call minutes or a SIM in the phone.