Tech Blog

Seem to be on a roll with Sox tonight. Also figured out how to normalise audio files nicely.

The first thing to do with sox is to get it to calculate the max volume adjustment possible:

This will return a number like: 4.234

You can then call sox again using this number:

And if you're feeling particularly good you can put the whole command on a single line as follows:

Easy when you know how.

However, this time I finally managed to get past all the hurdles and jump through all the hoops to make this work.

Scenario is a follows. Audio file is comes in in alaw or ulaw format and we want to trim any silence before and after it.

First step is to convert it from alaw to pcm encoded wav file as SOX has issues filtering silence in alaw files

Then we do the trimming in one fell swoop.

A huge thanks to this article for giving such a thorough overview of the how silence detection works in sox.

Too easy, when you know how :-)

This sets turns it on for everything except gif,jpeg,png or mp3, as these are already well compressed.

Cheers, Mark

In order to come up with a reliable solution to this we decided to use the SSH server we had available and tunnel the windows sharing across the local port forwards, much simpler and more reliable.

Thanks to this article it was a breeze to set up.

Steps are as follows:

• Create loopback adapter on windows
• Configure loopback adapter on windows
• Reboot
• Configure SSH connection
• Test it all out

Create loopback adapter on windows

We'll give your computer an additional (fake) IP address, and we'll port forward to that address instead of the computer's real IP. Windows XP will continue to do file sharing on the real IP address. We'll assign it an IP of 10.0.0.1 (that's what we configured putty to use above.)

1. System->Control Panel->Add Hardware
2. Yes, Hardware is already connected
3. Add a new hardware device (at bottom of list)
4. Install the hardware that I manually select
5. Network adapters
6. Microsoft , Microsoft Loopback Adapter
7. (Go through the installation procedure.)

Configure loopback adapter on windows

1. Open your new fake ethernet adapter (Network Connections) , enter a made-up IP address (I suggest 10.0.0.1, which is a privately routable address that most folk don't use.)
2. Enable Client for Microsoft Networks.
3. Disable File and Printer Sharing for Microsoft Networks
4. Enable Interent Protocol (TCP/IP)
5. Click on properties for TCP/IP.
6. Enter your chosen IP address (10.0.0.1), subnet mask (255.255.255.0). You can leave gateway blank.
7. Under advanced->WINS, Enable LMHosts Lookup and Disable NetBIOS over TCP/IP

Reboot

Configure SSH connection

• Download Putty
• Enter IP address
• Enter Auth Key (if using SSH keys)
• Enter Port forwards for: (these connect the ports on you local machine to
  • 10.0.0.1:137 to 127.0.0.1:137
  • 10.0.0.1:138 to 127.0.0.1:138
  • 10.0.0.1:139 to 127.0.0.1:139
  • 10.0.0.1:445 to 127.0.0.1:445
• Save the config.

Test it all out

• Open putty, load the settings and connect.
• Open Exporer and type in: \\10.0.0.1\

You should now be connected to your remote windows system over a secure encrypted tunnel.

Cheers, Mark