# tcd

tcd is a hybrid digital voice transcoder for ham radio used by the new URF reflector.

## Introduction

This will build a new kind of hybrid transcoder that uses AMBE DVSI-based hardware for vocoding digital voice streams used in DStar/DMR/YSF *and* David Rowe's open-source Codec2 used in M17 as well as the open-source P25 vocoder, IMBE.

This is the only transcoder that will work with the [URF reflector](https://github.com/nostar/urfd).

This software is loosely based on LX3JL's **ambed**, but is easily different enough to be considered an entirely original work. Here are some major differences with ambed:

- tcd uses both hardware-based and software-based vocoders, providing a bridge between the closed source vocoders used in DStar, DMR NXDN and YSF and open-source vocoders used in M17 (Codec2) and P25 (IMBE).
- *UNIX Sockets* are used to communicate between the reflector and this transcoder. This greatly simplifies the code and significantly improves transcoding performance.
- Each configured module has a dedicated encoding and decoding instance running on a different thread. This prevents overloading when processing multiple voice streams and provides the best possible performance for the reflector's clients.

## Constraints and Requirements

Currently, this program must be run locally with its paired URF reflector. Remote transcoding is not yet supported.

Only systemd-based operating systems are supported. Debian or Ubuntu is recommended. If you want to install this on a non-systemd based OS, you are on your own. Also, by default, *tcd* is built without gdb support.

The P25 IMBE software vocoder library is available [here](https://github.com/nostar/imbe_vocoder). See its README.md file for instructions for compiling and installating this library.

If you are running tcd on an ARM-base processor, you can opt to use a software-based vocoder library available [here](https://github.com/nostar/md380_vocoder) for DMR/YSF vocoding. This library is used for the AMBE+2 (DMR/YSF/NXDN) codec. If you are going to use this library, *tcd* must run on an ARM platform like a RPi. Using this software solution means that you only need one DVSI device to handle D-Star vocoding.

The DVSI devices need an FTDI driver which is available [here](https://ftdichip.com/drivers/d2xx-drivers). It's important to know that this driver will only work if the normal Linux kernel ftdi_sio and usbserial drivers are removed. This is automatically done by the system service file used for starting *tcd*.

## Download the repository

In the parent directory of you urfd repository:

```bash
git clone https://github.com/nostar/tcd.git
cd tcd
```

To be perfectly clear, the urfd reflector repository clone and this clone **must be in the same directory**.

## Compiling and configuring *tcd*

 Copy the three configuration files to the working directory:

```bash
cp config/* .
```

Use your favorite text editor to edit the following files:
- *tcd.mk* defines some compile time options. If you want to use the md380 vocoder, or change the installation directory, specify it here. Once you've set these options, do `make` to compile *tcd*. If you change `BINDIR`, you need to also change the `ExecStart` in your *tcd.service* file.
- *tcd.ini* defines run-time options. It is especially imporant that the `Transcoded` line for the tcd.ini file is exactly the same as the same line in the urfd.ini file! Suggested values for vocoder gains are provided.
- *tcd.service* is the systemd service file. You will need to modify the `ExecStart` line to successfully start *tcd* by specifying the path to your *tcd* executable and your tcd.ini file.

## Installing *tcd*

It is easiest to install and uninstall *tcd* using the ./radmin scripts in your urfd repo. If you want to do this manually:

```bash
sudo make install
sudo make uninstall
```