Converting recorded sound (text file) back into playable audio?

[toppe]

Hi all, I am new to the forums here and looking for some help.

I have a lot of stored data from measuring noise generated by various pieces of machinery. This is recorded by a G.R.A.S. microphone and read into the computer by Labview hardware and interface. The measured data is then written to a text file at 49kHz sampling.

My question is this: is there a way to convert this back into a playable audio format? My engineering sense tells me that there should be an easy way since all of the necessary information is present in the file. However, the google approach failed me here since the search results using relevant words almost entirely point towards speech-to-text converters or various audio converter softwares.

Any help or relevant links would be much appreciated. Thanks!

[twotoedsloth]

Have you tried importing the data in raw format, in Sound Forge? You might have to load your data into Excel first to sort the information.

[Madman_Greg]

I'd be surprised if these files were text.

http://www.ni.com/white-paper/4139/en

[Richie Royale]

Based on Madman Greg's link, it looks like the files are ASCII text files, so I don't think there is any audio data to be extracted, but I am far from knowledgeable about technical things like this.

I would have a good look on their website

http://www.ni.com/support/

[Madman_Greg]

but I am far from knowledgeable about technical things like this.

Neither am I, the last time I worked with data logger technology was back around 1986

Was interesting to see how it has moved on though...

[BJG145]

It sounds like there's a way to convert between WAV files and LabVIEW waveform data, so it may be possible to resurrect the audio using LabVIEW if you have the right files.

http://cnx.org/content/m14771/latest/

[toppe]

Thanks for the quick responses.

Have you tried importing the data in raw format, in Sound Forge? You might have to load your data into Excel first to sort the information.

I'd be surprised if these files were text.

http://www.ni.com/white-paper/4139/en

At this point, I do not think it is a ni issue. The text files were written as ASCII by a custom assembly code written by my predecessor. There is a short header which lists operator name and such and then four columns of tab-separated data; time, and three (scaled to Pascals) microphone signals. I can manipulate this file however is necessary, but the question put more precisely is "can a column of pressure values and known sampling frequency be encoded as playable audio?" I am not familiar with raw format, if raw can be converted to other types and can be created by simply formatting text, then that might be my best option.

It sounds like there's a way to convert between WAV files and LabVIEW waveform data, so it may be possible to resurrect the audio using LabVIEW if you have the right files.

http://cnx.org/content/m14771/latest/

I think I will try this, thanks!

Any other suggestions would be still be very welcome. Thanks again for the advice.

[ken long]

I can manipulate this file however is necessary, but the question put more precisely is "can a column of pressure values and known sampling frequency be encoded as playable audio?" I am not familiar with raw format, if raw can be converted to other types and can be created by simply formatting text, then that might be my best option.

SPL values will not be needed for this but sample rate will. Someone mentioned Soundforge. Another free equivalent is Audacity (http://audacity.sourceforge.net/). This is a free download and will open RAW files provided you supply the header with bit depth, sample rate and channel count. Then it's just a question of "Save As" your desired format.

[BJG145]

The text files were written as ASCII by a custom assembly code written by my predecessor.

If the data was generated by a custom program, then even assuming that it contains enough information to recreate a WAV file, you'd clearly need a custom program to do the conversion. Sounds like a lot of effort - what's the purpose...?

[toppe]

SPL values will not be needed for this but sample rate will. Someone mentioned Soundforge. Another free equivalent is Audacity (http://audacity.sourceforge.net/). This is a free download and will open RAW files provided you supply the header with bit depth, sample rate and channel count. Then it's just a question of "Save As" your desired format.

Thanks Ken. I have Audacity installed now. However, I am struggling to figure out what options to use when importing the raw data. Audacity prompts asking for bit encoding, byte order, channels, and sample rate. Do these have to be present in the header of the text file as well?

In order to test how the program works, I created a 440Hz sine wave in Excel with 5000Hz sampling and saved as a text file. I have tried a few different import settings, but the waveform showing up in Audacity is not the sine wave I generated. Is someone willing to try importing this as raw from a text file to help me figure out what settings to use or how to format the data differently? I do not see a good way to post a long string of values or attach a file on the forums here. I will post it if someone is willing to try it and can tell me a way to share the file with them.

[Madman_Greg]

The way I understand is as follows.....

RAW audio files do not contain any header information

As there is no header, compatible audio players require information from the user that would normally be stored in a header, such as the encoding, sample rate, number of bits used per sample, and the number of channels.

So if your code stripped those out, then you will need to know how they were encoded in the first place

[James Perrett]

If I was doing this I'd write a C program to do the translation. If you don't know C then Matlab may offer an easier alternative.

James.

[Madman_Greg]

Download a sine wave MP3

Put into audacity

Use the analyze / sample data export function

See what it produces - compare with the file you have

Use a number of different export options, to see the different, i.e. with header, headerless etc...

Might help you progress

[Jim Lockhart]

MatLab will import an ASCII text file into a MatLab variable. You can then plot the variable to see if it looks like a waveform. Then, use MatLab's wavwrite function to export a standard wav file; see this link http://www.mathworks.com/help/matlab/ref/wavwrite.html

[toppe]

MatLab will import an ASCII text file into a MatLab variable. You can then plot the variable to see if it looks like a waveform. Then, use MatLab's wavwrite function to export a standard wav file; see this link http://www.mathworks.com/help/matlab/ref/wavwrite.html

Wow, thank you so much! This solution was exactly what I what I needed and incredibly simple to implement in matlab.

data=load('noise.dat');
pressure=data(:,2);
Fs=1/(data(4,1)-data(3,1));
wavwrite(pressure,Fs,'sound.wav')

Thanks to everyone for the kind help, it looks like this works well to solve my problem. It converts a two column text file with time in the first column and pressure waveform in the second column into a playable .wav file.