Downsampling with sox

[Christina S]

In the instructions, you say that

if we recorded at 24bits instead of 16bits, we should use sox to change the bit depth, and we can downsample at the same time using sox instead of ch_wave:

bash$ sox recordings/arctic_a0001.wav -b16 -r 16k wav/arctic_a0001.wav

Which is the flag I need to use to downsample at the same time? Does the flag -r indicate the original recording sampling rate (in which case I would have to change this to 48k) or the target downsampled rate?

Thanks 🙂

[Simon]

-r indicates the sampling rate of the output file. sox will automatically determine the sampling rate of the input.

[Christina S]

Thanks Simon. I realised I had also recorded with 2 channels so needed to discard 1. Now I’m running something like:

bash$ sox recordings/arctic_a0001.wav -b16 -r 16k wav/arctic_a0001.wav remix 1

Now it seems like the files in the wav directory are much bigger (68.7 MB each) compared to in the recordings directory (1.1 MB each). Where am I going wrong? I expected them to be much smaller in the wav dir.

This is causing problems when I get to do_alignment. It’s throwing an AllocBlock error.

[Simon]

Run soxi recordings/arctic_a0001.wav to see information about that file format, and post the output here. If you wish, attach one file, such as recordings/arctic_a0001.wav to your post so I can investigate.

[Christina S]

This is the output from soxi:

Input File : ‘recordings/arctic_a0001.wav’
Channels : 2
Sample Rate : 48000
Precision : 24-bit
Duration : 00:00:03.84 = 184320 samples ~ 288 CDDA sectors
File Size : 1.11M
Bit Rate : 2.31M
Sample Encoding: 24-bit Signed Integer PCM

I’ve attached a sample file too.

Attachments:

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[Simon]

bash$ sox recordings/arctic_a0001.wav -b16 -r 16k wav/arctic_a0001.wav remix 1

works as expected for me on your file.

Use soxi to inspect your output file: does it have the expected sampling rate, bit depth and duration?

One explanation for the large size of your output file could be that you accidentally combined multiple files, which would happen if you did this:

bash$ sox recordings/*.wav -b16 -r 16k wav/arctic_a0001.wav remix 1

[Author]

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