Issue with Converting MOno to Stereo

Hello All,
I am trying to write an application tat can extract the audio data from multiple files and create a single audio file. For this , I needed to ensure that all audio files are in the same format.
As the files I received had been recorded on multiple devices, some in mono some in stereo, etc I used audacity to get all files in same identical format stereo 44100Hz 32bit float and saved as windows 16bit PCM wav files.
The technical issue I am faced with comes next.
After all files are in the same format, I ran a windows program to check the file information to ensure that all files are in identical format.
However I notice that some files still show with 1 channel and some with 2 , files have different sampling rates.
Shouldnt the metadata information get updated when I export files out of audacity ?

How did you do those two things?

Did you set the project rate in the lower-left corner of the Audacity window?

How did you create the stereo track from mono?

Shouldnt the metadata information get updated when I export files out of audacity ?

It’s very-very unlikely for the header information is wrong (that it doesn’t match the actual file). If the header doesn’t match the actual audio data the file will play at the wrong speed. It will play at the wrong speed if the sample rate is wrong, and it will play at double or half-speed if the mono/stereo information is incorrect.


For uncompressed files, the file-size can be a clue. As you may know, there are 8 bits in a byte. i.e. A 16-bit stereo file has 4 bytes per sample. If the sample rate is 44,100 samples per second, you have 176.4k bytes per second of sound. Of course a mono file will be half the size, and if the sample rate is wrong the file size will be proportionally smaller or larger.

The name of that Windows application?

You need to change the project rate bottom left of Audacity to set the rate you want to export at.

It varies from format to format, but the digital audio properties are not normally stored in metadata tags but in the headers (as Doug says). Many players don’t even read metadata tags in WAV files.

Do you really want to convert from mono to stereo, making two identical left and right channels, or from stereo to mono? A mono file will play equally through both speakers of a stereo system.


To clarify some questions -

  1. I am duplicating the mono channel as another channel and converting to stereo.
  2. I change the project rate to 44100 in left bottom corner and resample the stereo before I export.
  3. I mean to say "header when I said metadata.- my bad.
  4. The windows application I have written examines the file contents starting from the RIFF header upto the DATA segment and process it.
    While doing that some files show up as stereo and some as mono…
    The [Format Chunk Size] and [isPCM ? ] show up correctly but [Num of Channels] and [Sample Rate] differ.
    Definitely need these 2 to be same as the next application which is going to use the audio files is merging the audio data to create a single file out of multiple such audio files and needs all data to be in same sampling rate and stereo.
    ANy hints where can I post the program that examines the audio files for accuracy ? Not sure if its within the scope of the forum.
    Is there any other tool that can run through about 700 such files and show which files are different and what needs changing ?

I need to process about 700 audio WAV files to make sure all have 2 channels, and identical sampling rate @ 44100 32bit float and exported as windows 16bit PCM WAV files.
Any tips on how I can do this ?

If I understand correctly, this is the same task as that already in this topic, so to avoid confusion I moved this post here.


Why? Mono will play in both channels of a stereo player.

What does “resample the stereo” mean? If the files are not at 44110 Hz originally, you don’t need to do Tracks > Resample… to export as 44100 Hz. All that is needed to export at 44100 Hz is to change Project Rate to 44100 Hz.

Even if that application is not functioning correctly that is not an Audacity problem.

Not an Audacity problem.

It isn’t :wink:

But you could use any number of tools to get information about the file. You could use “MediaInfo” from MediaInfo - Download MediaInfo for Microsoft Windows. Get the version without installer, because the installer may have malware or adware.

However is there a reason you don’t use Audacity for this? Audacity shows you the sample rate and stereo or mono in the Track Info. It does not show you the bit depth the file has, rather the bit depth at which Audacity is reading the file. But if I understand it, that does not matter to you.


I would just use dBPowerAmp to list the file properties and batch process the conversion. You can set it to stereo conversion, so if the file happens to be mono, the mono track will be duplicated to two stereo channels. You can set the sample rate and the bit depth.

You can also use SUPER player but it can be a complex task to figure how to download it.


Thanks for the replies and suggestions, I will explore the mediaInfo link that was shared.

The final outcome required is to have all audio files with same bit depth, sampling rate and channels.
This will ensure that the program that joins the audio files, doesnt have to do the processing of the bit depth, sampling rate and then extract the audio data based on the target bit depth and sampling rate.
I need 2 things -
one a utility to batch process the 700 odd files so that i dont have to do the conversion one by one in audacity.
one utility that can scan these 700 files to tell me that all files are with same bit depth, sampling rate and channels - again to save processing time in final application which may have to splice upto 100 or more such files and stream the audio data over the internet, to be interpreted and played back by a HTML5 and jQuery based player.

Gale, Looks like dBPowerAmp is doing what is required.

Yes I think so. I usually batch convert with it by right-click over files, but I now remember it includes a “Batch Converter” application that will list the properties of files in a table, so you could verify the files that way.


To be clear, Audacity will batch process files ( Chains - for batch processing and effects automation ) but it can’t batch-verify file properties. Audacity imports a PCM copy of each file which then lets you run complex effects on each file in the Chain, but that takes time so if you just want to do file conversion, other utilities will be faster.