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calted · Location: USA Posts: 3

After downsampling some audio files of talk radio to save on disk space, I find flat line gaps between voice spurts even when recording back up to the 44 khs 32 bit sampling rate.

What happened?

jonrose · Location: USA Posts: 2901

From your description, I don't really get a clear picture of what you're experiencing...

Without further clarification, though, I'd venture a guess that if you were whacking the bit depth also, then there's certainly the possibility of quantization effects, which obviously would not go away if you converted it back to a file with better resolution - much like lossy compression, the damage would already be done.

If you could be more specific about what you're doing and the specific results, perhaps someone could offer some further thoughts.

Best... -Jon

calted · Location: USA Posts: 3

Thank you for responding Jon. I'm sorry I wasn't clear.

The files that I downsampled were okay. Degraded in quality as one might expect but with no oddball artifacts.

It seems that with all subsequent recordings at any sample rate and bit depth, that during the normal pauses within normal speech, the waveform is "straight line" (absolutely silent) with no background noise. Somewhat like a radio squelch that is set too high. I hope I didn't lose you with that one. Or let's try this; An automixer with the sensitivity set so that the channel turns on too long after the sound begins and cuts off too quickly after the sound ends. Too bad I can't attach a few seconds of the waveform.

Another possible example might be the waveform that results when CE noise reduction is used too aggressively.

For months, all was well until I started downsampling and somewhere along the line, some setting got changed but I never recorded the original defaults so I'm clueless as to what might have changed. Maybe I ought to strip CE off my machine and reinstall it which should take me back to the original default settings?????

Thanks in advance for any advice!!

SteveG · Location: United Kingdom Posts: 6695

All depends how much you downsample them, and far more significantly, whether you altered the bit rate at the same time. Every time you drop the bit rate, the ultimate noise floor gets higher... If you dropped the bit rate to 8-bit, then it's quite possible that you could have a greater dynamic range on your signal than you could reproduce with 8 bits - i.e. 48dB. That would give you a flat line noise floor!

calted · Location: USA Posts: 3

Hello Steve.

I read your post early today while at work and had to wait till now to reply.

Thank you for your info. I think you nailed the problem.
When I record my stuff at 44khz and 32 bits and later downsample to 11 khz and 8 bits, the quality seems to hold up much better than recording the same audio directly to 11 khz and 8bits. As you said, the dynamic range of my material exceeds the capabilities of those settings but for some reason, the problem does not show up when downsampling from a 44 khz 32 bit file of the same audio.

Also under the settings options in the software (under "DATA"), I found the downsampling and upsampling quality levels at one hundred something. I increased them both to 1,000 and it seems my problem went away.

Thank you again for your input and also to Jon on the previous post.
I will be looking in on these forums regularly. There are a lot of knowledgeable people here and the wonderful thing is that you are willing to share your knowledge! Thank you again!