IHU Manual Page

2.2.1 General settings

• My name: here you can write your name, nickname, address, or whatever you want that your partner will see in order to recognize you. In my opinion it's important to write something here, but feel free to leave it empty.
  
• Wait for incoming calls at startup: if you prefer to start immediately waiting for calls when you launch IHU, without need to click on Wait for calls button, you can enable this option.
• Answer automatically the calls: with this option you have the possibility to directly start the conversation when receiving new incoming calls, without need to click the Answer button. This is useful for example if you want to receive calls but you're too busy to use the mouse or keyboard to click the button.
  N.B. When IHU automatically answers, it will start to send to your partner what is capturing on the microphone (unless you disable the audio input), so be careful to not use this option when you actually can't answer the call!
• Show tray icon: to enable/disable the IHU system tray icon. The tray icon is useful if you need to have a quick access to IHU buttons without need of keeping the window visible.
• Start minimized: when you enable the system tray icon, you have the possibility to launch IHU without opening the main window. This is useful, for example, when you enable IHU auto-run at system startup.
  
• Record stream to file: to record the audio stream to a ".ihu" file. At the moment IHU just dumps all the data packets to file, then you can play this file using the Play file function. Remember that if you record a crypted stream, then you won't be able to play it, unless you know the encryption passphrase.
  Unfortunately, at the moment, it is possible only to record the incoming stream seperately from the outoing stream. This means that your voice will be recorded to one file, while your partner's voice will be recorded to another file. But this is already useful for example to:
1. Record messages when you can't answer calls (see the Ring button above)
2. Save important converstations, so that you can listen them again in the future whenever you want.
   

2.2.2 Network settings

• Receiver allowed protocols: here you can choose which protocol you want to enable on your Receiver. IHU is using both UDP and TCP by default (recommended), so that callers can choose their preferred protocol, but you have the possibility to disable the protocols that you don't want to use. Of course you have to enable at least one protocol to receive calls.
  
• Reveiver port: this is the UDP/TCP port number on which your IHU is receiving calls (default is 1793). Please note: this port is very important and usually you shouldn't change it. If you really need to change this port, please make sure that your callers know your new port number, otherwise nobody can call you. In order to use ports lower than 1024 you must have root privileges.
  


• Caller preferred protocol: this is the protocol used for outgoing calls (only one protocol is possible for each call). If the Receiver you want to call has both TCP and UDP enabled, then you can choose your favourite protocol, otherwise you have to use the protocol chosen by the Receiver. If you receive errors like "Connection refused" or "Connection rejected" when makine a call, try to change the protocol.
• Caller port: this is the port number of the Receiver you want to call. Please note: usually you don't have to change this port, but if the Receiver is using a different port number (and he should have told you), then change it.
  

2.2.3 Sound settings

• Sound driver: here you can choose the sound driver used for input (capture) and for output (playback). By default IHU is using ALSA for both input/output, but if you have JACK sound driver installed on your computer, then IHU should have compiled with JACK driver support. This means that you can also choose to use JACK as input and ALSA as output, or JACK for input/output (note that you can't use ALSA for input and JACK for output).
  A little note for JACK sound driver: Jack can give better sound performance (against audio latency), but requires  a little more attention: please make sure that your Jack server is properly configured for IHU (i.e. the same sample rate, sample width, buffer size, etc..) and that when you start playback or recording, IHU Jack ports are properly connected to capture and playback devices. Note also that when using Jack as output driver, the ADR option is not available (there is no need! ;-).
• Sound interface: here you can choose the input and output interfaces for ALSA. For each sound card ALSA offers two interfaces, hw and plughw. If you have more than one sound card, you can change the sound card, giving the right device number (for example plughw:1).
  Please note: this setting is VERY important for IHU, so I strongly suggest to select the interfaces which work better for your computer. The default interface used by IHU is plughw, which should give better performance and low latency. However the plughw interface has one disadvantage: it doens't allow more than one capture stream per time (and eventually also playback, depends on your soundcard). So if you need to use other capture programs, then you have to choose another interface which use the dsnoop plugin; or if have other kind of problems then try to change the interface (try first the hw interface, which gives direct hardware access, then the default interface, or other custom interfaces). Anyway, if you decide to change the interface, than you're responsible to check the ALSA settings (read ALSA documentation for more informations on how to configure ALSA), and keep in mind that the performance of IHU could get really worse (long delay and bad sound quality) if you choose the wrong interface. I recommend the use of plughw/hw or the Jack sound driver, where possible.
  
• Input format: to change the audio quality (adjusting input sample rate and format). At the moment only three rates are possible (according to Speex rates): 8000 Hz (low quality), 16000 Hz (medium quality) and 32000 Hz (high quality). The higher the quality, the higher the use of network.
• When silence is detected continue TX for (seconds): when you are using a threshold greater than zero, it's useful to continue the transmission for some seconds, to preserve the stream against small speech pauses.

2.2.4 Encoder settings

• Bitrate mode: you can choose a Constant Bitrate (CBR), where bitrate stays constant during the communication, using always the same amount of outgoing traffic (adjust bitrate with CBR Quality, see below). Or you can choose a Variable Bitrate (VBR), where the encoder decides automatically which bitrate to use for each frame, according to the complexity of data (adjust bitrate with VBR Quality, see below). Or you can finally choose an Average bitrate (ABR), that is a kind of variable bitrate, but the average bitrate is constant (adjust bitrate directly with ABR kbps parameter, see below).
  
• CBR Quality: to select the bitrate for CBR (1: lowest quality, 10: highest quality).
  
• VBR Quality: to select bitrate for VBR (1: lowest quality, 10: highest quality). Higher quality means higher bitrate, but due to variable bitrate, it can be lower or higher than what you chose, depending on the complexity of audio signal to be encoded.
  
• ABR kbps: to select an average bitrate for ABR (Kbit/second). Bitrate is variable but the average should be around the value you specified.
  
• Complexity: it is a parameter to select the algorithmic quality. (1: lowest, 10: highest). Higher complexity means also higher CPU use.
  
• Voice Activity Detection (VAD): when enabled, it detects whether the audio being encoded is speech or silence/background noise. VAD is implicitly activated when encoding is VBR.
  
• Discontinuous TX (DTX): it's an addition to VAD/VBR operation, that allows to stop transmitting completely when background noise is stationary.
  

2.2.5 Options settings

• Time change percentage: this is the time percentage (0-50%) that determines the speed of delay adjustment. With a high time stretch, the delay will be adapted faster, instead with a small time stretch, the delay will be adjusted more gradually (suggested, because a time stretch too high might damage the sound quality or might render the speech incomprehensible, or just too fast ;-).
• Minimum delay: this is the minimum delay (milliseconds). When ADR is activated, if the delay on the playback sound interface is smaller than this value, IHU will try to increase the delay to this reference value, in order to avoid sound crackle.
  
• Maximum delay: this is the maximum delay (milliseconds). If you activated ADR, IHU will try to minimize the audio delay to this value. Be careful with too little values of max delay, which could deteriorate the sound quality, or with values of Maximum delay too near to Minimum Delay, give at least 40/50 ms of tolerance.

• Volume change speed: this is the speed factor (1-100) of playback volume adapting, in order to reach the reference volume value (the one you control in the main window, see above). Increase if you want the volume to adapt faster, reduce to make the volume change more gradual.
• Minimum gain factor: this is the minimum amplification factor, to soften the sound. A value of zero means that sound can be reduced to total silence. Instead, if you don't want to reach silence, than increase this value.
• Maximum gain factor: this is the maximum amplification factor, to amplify the sound. You should decrease this value if silence is amplified too much and the sound gets too loud and distorted when user is speaking, instead increase if the volume is not well amplified enough.

2.2.6 Security settings

• Encryption key type: you can choose the type of key used for the symmetric encryption (Blowfish) of your data. You have two possibilities:
1. Random with constant length: if you choose a random key, than IHU will automatically choose a new random key each time you enable Encrypt outgoing stream, or each time you Change the encryption key. You can choose the length of the key (in bits); bigger keys should be more difficult to crack. Please remember also that with a random key it will be impossible to play recorded streams.
   
2. Text passphrase (please use phrases of at least 30 chars, max 56 chars): each time you enable Encrypt outgoing stream, or you Change the encryption key, IHU will ask you to enter a new passphrase, that will be used for encryption. This is useful, for example, if you want to record the crypted stream to file and you want to have the possibilty to play this file later with IHU (instead with a random key it's not possible).
• Show decryption key of incoming stream in the Log: this option will show the decryption key type, and eventually the passphrase, of the incoming stream in the Log. When the incoming stream is using a new encyrption key, then a new message will appear in the Log, and if the key is a text passphrase, then it will be showed, otherwise IHU will just write "random key". This is useful if you are recording the stream and you want to be able to play the stream with Play File option. Since the passphrase is a confidential information, if you don't need to know the passphrase, then please do not use this option.
  
• Write a copy of the Log also to file: if you want to save the Log (the one you open with View Log button) to file. This is useful if you want to save call informations for the future, or if you want to carefully log all incoming connections and calls (for security reasons).
  N.B Please take care of this file because it could contain confidential informations!

3. Quick launch

USAGE
        ihu [OPTIONS]
OPTIONS
        --wait          Wait for incoming calls
        --call  HOST    Call the host with specified address
        --file  FILE    Play the specified file
        --encrypt       Encrypt the outgoing stream
        --noinput       Disable audio INPUT
        --nooutput      Disable audio OUTPUT
        --nogui         Start without GUI (no interaction)

4. Final notes