IHU Manual Page
Welcome to I Hear U
(IHU), a Voice over IP (VoIP)
application for Linux, that creates an audio stream between two computers easily and with
the minimal traffic on the network.
The main features are:
communication takes place directly between the computers (UDP and TCP
both supported), without need of session protocols (such as SIP or H323)
or other servers in the middle.
Good audio performance: IHU
was born to give the best audio performance, low latency above all. For
this purpose IHU is compatible with ALSA,
now the default Linux sound architecture, but also with
JACK, a low latency sound
server. For the audio compression, IHU uses Speex,
a codec optimized for speech (and completely free and open source).
Crypted stream: you have
also the possibility to Encrypt/Decrypt the stream using a fast hybrid
cryptographic system (RSA + Blowfish)
the Qt GUI is not strictly necessary, you can run also a textual IHU
from command-line (for example if you need to run the program on remote
Free and Open Source: IHU
is totally free and distributed under the terms of the
GNU General Public License.
The possibilities of use of IHU are endless, for example you can use it
like a phone to talk with your friends all around the world, or at home/work
to talk between computers in the LAN (talkback), etc.
1.1 Some important notes before starting...
First of all make sure you have the latest version of IHU (http://ihu.sourceforge.net
Follow the instructions contained in README and INSTALL files to compile the sources (you'll need the
, the ALSA
sound driver, the Speex
and the Ogg
Anyway the automatic configure script will tell you what is missing.
If you want to transmit your voice/audio, then you need a
microphone linked to your computer (but it's not necessary to use IHU)
and, finally, you need a person to talk with, who has a computer linked to you (through
the Internet or LAN) and IHU installed as well (unfortunately IHU it's
not so useful alone on your computer, even if I spent hours talking to myself for tests ;-).
Finally, I suggest to use headphones, to prevent feedback.
IHU's way to work is similar to a telephone: there is somebody who is
waiting for phone calls, and somebody who wants to call this person.
In the next paragraphs, the computer that will make the call
will be named Caller
and the computer
that will receive the call will be named Receiver
Now the next two steps are external
to IHU and are necessary before continuing: setting up the network and the audio system.
1.1.1 Network settings
You need to know how your network is organized (is there any firewall between you and your
IHU partner?). The most important thing is:
If you want to receive
calls, then your computer must be able to receive incoming connections.
Those situations are possible:
If your computer is connected directly to Internet (or LAN)
and Callers can access it
directly with an IP or DNS address, then you should be ready to make calls without problems.
If your computer is connected through a gateway with NAT and/or a firewall, then:
in order to receive calls, you have set
up the firewall/gateway rules to forward incoming connections to 1793
TCP/UDP port (default, but you can change it from IHU settings).
Instead, in order to make
calls, you have to make sure that the firewall (usually possible) is allowing
outgoing connections on port 1793 (TCP and/or UDP).
If you can't change the rules and you have a very strict
firewall that allows only outgoing connections to important ports like 80, 25, etc.,
you could change the port of IHU to those allowed
ones, but then you have to ask the Receiver
to change his port, and for those port he needs root privileges.
If both computers are accessible from each other's IP address, no
problem, both can receive and make calls.
If one computer (or both) computers are behind firewall but you
could change the rules as described abow, still no problem.
If one computer is behind firewall and you can't change rules,
then on this computer you can't receive calls, but you can still make
If both computers are behind firewalls and it is not possible to
change any rules (it seems that you are very unlucky!), then you have
no chances to talk to your friend :-(
: You can easily test if
everything is fine using the netcat
runs "nc -l -p 1793" (or for UDP "nc -u -l -p 1793"), and
runs "nc RECEIVER_IP_ADDRESS 1793" (or for UDP "nc -u RECEIVER_IP_ADDRESS 1793"). If you can see what your
partner is typing (and viceversa), then IHU won't have any kind of problems.
1.1.2 Audio Settings
Then you need to set up the audio mixer, selecting the audio
source and the optimal volumes. To do this you can open any mixer
program (like "kmix" for KDE), paying attention to the recording
source, that usually should be set to Microphone if you want to send your
voice, and to the recording level (that for ALSA is usually named
"Capture"). Also, take note of the playback volume (usually named
"PCM", the one that you control also with XMMS, for example), because
if it's too low, it will be hard to hear your partner.
You can easily test the
audio settings directly with IHU. Click on Wait for calls
button and then call yourself by typing "localhost" as receiver address and clicking the
You will now hear yourself and you can check settings.
But read the quick start to know how to do this if you have problems calling.
1.2 Quick start
Ok, you are ready to use IHU! Now you just need to know the
address (IP or DNS) of the friends to call.
Each IHU user who wants to receive calls should give his address to his
IHU friends. Personally, I strongly suggest to register to a dynamic
DNS service (such as dyndns
you can register your computer with a fancy DNS address easy to
remember (such as ihu.homelinux.org
then each time you go online, your IP should update and your
friends can always call you with that address.
Let's suppose now that your internet address is ihu.homelinux.org
and that you want the receive calls from your friends. Then, first of
all, you have to run IHU and press the Wait for calls
button. Your friend
now will type ihu.homelinux.org
in the Receiver address
and will press the Call
Hopefully you will see an inbound call notification and sound and if
you want, you can answer by clicking on the Answer
button. At this point you should see the TX and RX leds flashing, and you
should hear something, now you can finally cry out: "I Hear U!!!" ;-)
2. Detailed description
2.1 The main window
The main window (see screenshot
) is composed by:
Receiver address: here
you write the address (IP or DNS hostname) of the computer that you
want to call, then press Enter or click the Call
button to start the communication. As port, IHU is using the default port in the Settings
(usually 1793), but if you want to temporarily use another port for a specific host
(without changing the default port in the settings), you can quickly specify the
port just after the IP address in the form ADDRESS:PORT
(for example to use the port number 1790 "ihu.homelinux.org:1790").
after you type the Receiver address,
click this button to start the communication. IHU will first ring the
Receiver and then, if he
answers, it will capture and send your voice to your partner and you
will receive your partner's voice. If your are Waiting
for calls and you received a new call, than this button will
become Answer (Alt+A),
and will allow you to answer the call.
(the button with a little bell between Call and Hang Up):
this is a special button. When you click this button,
your partner, instead of listening to your voice, will hear a nice
ringing sound, similar to the phone (it is usually so loud that could
eventually damage his ears ;-). To stop ringing just click the button again. The button is
available also during conversation, useful for
example when you want to notify you're back after a pause, or for other
many reasons you can think of. To disable the ringing tone when
receiving new calls, see the settings below.
N.B. IHU will automatically
activate this button when you make a call, and will stop ringing either
if your partner answers or refuses. But you can also stop ringing before,
without waiting for the answer clicking the
button manually. This is useful, for example, to:
- Let your partner recognize your voice, or call him by voice (funny, isn't it? ;-).
- Leave a message (like an answering machine) if your partner is recording calls (see below for details).
Hang up (Alt+H):
when you click this button, IHU will close the current communication.
If you are waiting for calls and you just received a new call, this button will become
Refuse (Alt+R) and you can refuse the call.
Wait for calls (Alt+W):
when you click this button IHU
will wait for incoming calls (remember that it isn't toggled by
default when you run IHU, unless you enable the proper option in the
When you receive an incoming call, IHU will NOT send your voice to
the caller until you press Answer.
If you don't want to receive calls, then just deactivate this button.
- TX led: this red led is on when IHU is transmitting data.
- RX led: this green ledis on when IHU is receiving data.
Disable audio input globally (Alt+I) (button with microphone): click
this button to disable audio capture or to mute your microphone for all the calls
Disable audio output globally (Alt+O) (button
with speaker): click this button to disable playback or to mute the speakers for all the calls (but incoming data
will be received anyway, and eventually recorded).
TX threshold: the volume
level (-96dB/0dB) to be considered silence. When the sound level is softer than the
threshold, IHU will consider that sound level as silence and won't send any data.
This allows you to save network bandwith when you are not speaking. You should change
this value to a suitable value so that TX led is off when you are not speaking. Of course this
does not affect the data that you are receiving.
Recording level: useful to monitor the current
volume level (-96dB/0dB) recorded on your sound card.
2.1.1 The FILE menu (Alt+F)
The FILE menu offers these simple functions:
New call (Ctrl+N): to create a new call tab.
When you create multiple call tabs you will be able to make and receive multiple calls at the same moment.
Close call (Ctrl+W): to close the current CALL tab.
If the call is active this operation will also close the communication. Note that the "Default" call tab
can't be closed.
File Player (Ctrl+P): this
button opens the File Player window. With IHU you have the possibility to save
the outgoing/incoming streams to a .ihu file and then play them using the File Player.
With the File Player it's also possible to convert .ihu files to .spx files.
Log Viewer (Ctrl+L): this
button opens the Log window. The Log is the place where IHU records some informations
about the incoming/outgoing calls, the address/name of the person who called you, the encryption
key used, and other informations. The log is cleared each
time you close IHU, but you can also save it to file using the proper button in the dialog
or you can always save a copy of this log to file (see settings below).
- Quit (Ctrl+Q): to quit ;-)
2.1.2 The CALL menu (Alt+L)
This menu contains functions that will affect only the call in the current tab:
Encrypt outgoing stream (Ctrl+E):
when you check this option IHU will encrypt the outgoing stream.
Your partner will be able to decrypt thanks to an automatic (and secure) key exchange.
You can check/uncheck this option also during the communication.
N.B. This option will only
affect your outgoing
traffic. The incoming traffic is independent and can be encrypted or not, it doesn't
matter. However, when one peer is encrypting the stream, then his
partner will be "invited" to do the same, automatically enabling
encryption too, but the user is always able to decide whether to crypt
or not. So you can disable this option at any time during conversation.
Change encryption key (Ctrl+K):
to change your encryption
key with a new key. You can change the key also during communication,
whenever you want (so IHU is compatible with paranoid individuals ;-)
Set/reset decryption key (Ctrl+D):
this is useful to reset the decryption
key or to change it, but, at the moment, it is only possible to set a text passphrase.
So if you need, for any reason, to set a different passphrase,
or you want to reset your decryption key in order to receive a fresh decryption key, then this
function is for you.
Record incoming/outgoing stream to file:
to record the audio stream to a .ihu file.
At the moment IHU just dumps all the data packets to file, and the if the file doesn't exist itwill be
created otherwise data will be appended to the file. You can only play a
.ihu file using the
IHU File Player (you can find it in the File menu).
Unfortunately, at the moment, it's only possible 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.
The .ihu files are useful also to:
N.B. If the recorded stream is encrypted, then you won't be able
to play it, unless you know the encryption passphrase
- Record messages when you can't answer calls (see the Ring button above)
- Save important conversations, so that you can listen them again in the future whenever you want.
Tip: to play multiple files together you can convert
them to .spx (See File Player)
and play them all at the same time using the speexdec program
(remember to set TX Threshold to minimum or to uncheck
DTX to avoid discontinuos TX when recording).
2.1.3 The OPTIONS menu (Alt+P)
The OPTIONS menu offers some interesting functions:
Audio Delay Reduction (ADR) (Ctrl+R):
since there might be a delay between the time you
receive the data and the time you listen through your speakers,
you may want to reduce this delay. Check this option to let IHU keep
the audio delay as minimum as possible (please see settings below for
Automatic Gain Control (AGC) (Ctrl+G):
check this option to activate an automatic system that keeps the recording level constant.
If your voice is too soft, AGC will amplify it, instead if too loud AGC will soften it
(please see settings below for details).
Please note: this option works well if
TX Threshold is properly set, otherwise when you don't speak
the silence will get amplified too much and when you start to speak again, the sound will become distorted.
Clear Host History (Ctrl+H): to clear the history of the
Receiver address field.
Clear Missed Calls (Ctrl+M): when you don't answer or refuse a call
IHU will show you an alarm icon in the tray and will notice that there are some missed in calls in the status bar.
Use this function to clear the tray icon and to set the missed calls to 0.
Settings (Ctrl+S): to
open the settings dialog and adjust IHU parameters (see below).
2.1.4 The HELP menu (Alt+E)
There are not so many things to say here, the only help available is
what you are reading now! ;-)
2.2 The settings dialog
You can access the settings dialog from the Settings
button in the main window or from the option menu (or Ctrl+S).
The settings dialog allows you to change all the parameters and
options of IHU, that are saved in a XML config file (default is
can also save the configuration file manually, using the
"Save to file"
button in the dialog.
The Settings dialog is organized in several tabs (please note that
the default button will set the default parameters only for the
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
Wait for incoming calls at startup:
if you prefer to be able to receive calls immediately when you launch IHU,
without need to click on Wait for calls button,
you might want to enable this option.
Answer automatically the calls:
with this option you have the ability to automatically answer a new
incoming call, without need to click the
Answer button. This is useful for example if you want to receive
calls but you're too busy to click the button.
N.B. When IHU automatically
answers, it will start to send to your partner audio captured by 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
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 to auto-run at system startup.
Max Call Number: this is the maximum
number of calls that it's possible to use at the same time.
Save Host History: this is the number of
host addresses savd from the Receiver Address history (use Ctrl+H to clear the history).
2.2.2 Network settings
This tab is divided into two parts. The first is about your
IHU as Receiver
receive calls), the second is about your IHU as Caller
(when you make calls):
Receiver allowed protocols:
here you can choose which protocol you want to enable on your
Receiver. IHU can accept 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.
Receiver 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
preferred protocol, otherwise you have to use the protocol chosen by
the Receiver. If you receive
errors like "call rejected" when making a call, try to change the protocol.
Caller default port: this is the
default port number for outgoing calls. If you don't specify any port after
the address in the Receiver address, then IHU is using this default port.
2.2.3 Sound settings
Sound driver: here you
can choose the sound driver for input (capture). 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, and you can also
choose to use JACK as input and ALSA as output.
A little note for JACK
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, etc..) and that when
you make a call, IHU Jack ports are properly connected
to capture and playback devices.
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 card
number (for example plughw:1,
please read the /proc/asound/card
file to know the card numbers). And, for each soundcard you can change
the device, giving the right device number (for example plughw:1,3, the /proc/asound/devices file contains
the device numbers). By default IHU is using the "default" interface,
which will automatically choose the best
interface and device for you.
Please note: the sound interface is VERY important for IHU, so I strongly
suggest to select the interfaces which work better for your computer.
The plughw and hw should give
better performance and low latency, but they have one disadvantage: they don't
allow more than one capture stream per time on the interface (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 you have other kind of problems then try to change
the interface (try first the plughw
interface, then the hw
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 can be greatly affected (long delay and bad
sound quality) if you choose the wrong interface. Anyway the Jack sound driver doesn't
have the disadvantages described above, have a look if you're interested.
to change the audio quality (by changing the sample rate). 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.
Stop TX after (silence secs):
when you are using TX Threshold to stop transmission
when you don't speak, it's useful to continue the transmission for some
seconds, to preserve the stream against small speech pauses.
number of packets to prebuffer before starting to play. A high number
of packets ensure audio continuity, but it could increase the audio delay.
Ring Volume: here you can adjust the volume of ring tone for incoming calls.
2.2.4 Encoder settings
Here you can change the settings of your Speex encoder
(so only for your
outgoing stream). Those settings are very important to determine the
voice and the use of network
so adjust them very carefully (please refer to the Speex website
for more details).
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.
TX Threshold will be disabled if you decide to not use DTX.
2.2.5 Options settings
Here you find some settings about the Audio
Time change percentage:
this is the time percentage (0-50%) that determines the speed of delay
adjustment. With a high time change, the delay will be adapted faster,
instead with a small time change, the delay will be adjusted more gradually
(suggested, because a time change too high might affect 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
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.
You find also some settings about the Automatic
(AGC) option. There are two methods of AGC, you can choose to
use only one of them, or you can use them together:
ALSA Mixer Control: this is the
first method of AGC. IHU will try to adjust the volume of the specified mixer control
(usually "Capture" on most sound cards) to reach the desired sound level.
This method is used by default and it's recommended because maintains a good audio quality,
since the gain is changed in the hardware. Disable this method only if
you don't want to touch the mixer levels.
IHU Internal Control:
this is the second method of AGC. IHU will amplify or soften the audio signal
using its internal routines, without touching the mixer levels.
Anyway the sound quality might be slightly damaged since the gain is virtually changed by software.
Volume Level: this is the volume level used as reference
by AGC. IHU will take the peak value of the recorded sample and will adjust the volume
according to this reference value.
Volume change speed: this value will influence
the rapidity of volume adjustment.
2.2.6 Security settings
Here you can find some settings about security and cryptography:
Encryption key type:
you can choose the type of key used for the symmetric encryption
(Blowfish) of your data. You have two possibilities:
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.
- Text passphrase
(please use phrases of at least 30 chars, max 56 chars): when
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).
here you have the possibility to save the passphrase in the config file so that it won't be asked
each time you decide to encrypt the communication; or it will be used if your partner is
using encryption and IHU will start automatically to encrypt. To clear the passphrase just leave
blank and press OK; instead to use a different temporary passphrase use the Change the encryption key
function in the Call menu.
Please note: the passphrase will be saved as cleartext in the config file, so be careful!
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
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.
N.B Please take care of this file
because it could contain confidential informations!
2.3 The file player dialog
The file player gives you the possibility to play a previously recorded IHU file (please above to know how to record a stream to file).
If the stream was encrypted than it is not possible to play the file at this time, unless you know its passphrase (IHU will automatically ask you the passphrase when encountering encrypted streams).
Open File (Alt+O): to open a IHU file to play.
Pause (Alt+P): this button will pause the file currently played.
Stop (Alt+S): this button will stop and close the file.
Convert .ihu file to .spx (Alt+C): this function is useful to convert
the files recorded with IHU (.ihu extension) to standard speex files (.spx extension). The .spx files are
standard Ogg files and are readable also by other applications, such as speexdec.
3. Quick launch
If you are a command-line lover, you have the possibility to launch IHU
with some quick launch options. Here is the list of available options (which you can get by starting with "--help"):
--conf FILE Use FILE as configuration file
--wait Wait for incoming calls
--call HOST Call HOST (DNS or IP address)
--file FILE Play a IHU FILE
--encrypt Encrypt the outgoing stream
--noinput Disable audio INPUT
--nooutput Disable audio OUTPUT
--nogui Start without GUI (no interaction)
As you can see there is one option (--nogui), which allows you to run IHU without GUI. This is
useful when you don't have the possibility to use a X server or when you want to launch
IHU on remote computers, but then you don't have any possibility to interact with the
program. I strongly suggest to use this option only for special cases, please use the GUI instead, which offers a
better interface (please note that when using --nogui you have to
change settings directly from config file, the default is "$HOME/.ihu.xml"
4. Final notes
Please use the Tracker
IHU sourceforge page
to report bugs, patch, support requests. For any other kind of
informations, suggestions, flames (ouch!), just mail the author.
Now enjoy IHU!!
Copyright (C) 2003-2008 Matteo Trotta <email@example.com>
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU
General Public License