Clarifications Re: MP3 File Size and Stereo vs Mono
A listener emailed me with some thoughts about my conversation with Todd Cochrane in episode 8. I thought my clarifications may be of some use:
1. Regarding the idea of reducing episode file size by reducing the sample rate from 44.1kHz to possible 32kHz, the listener wrote that this was an option, “…since you have a hard low-pass filter set in the neighborhood of 15K, …” My response: Not correct. I do use filters often but not as a rule, and not a HARD filter, and not always the same amount or the same frequency. And I only use filters on individual voices – not on the whole mix. So, I would never use a sample rate lower than 44.1kHz.
2. Regarding the stereo vs. mono conversation the listener wrote, “…Certainly, recording stereo output of a mono mic is pretty pointless and it sounds like you’d recognized that in the show…” I never recommended to record one microphone onto a stereo file – that’s ridiculous. The “stereo” we were talking about was the entire episode mix, where music can sound as it was made to sound (a carefully constructed presentation across the stereo spectrum) and individual elements/voices can be panned for more separation, clarity, etc.
3. Again regarding reducing file size, the listener suggested possible using VBR (Variable bitrate) MP3 compression. NOTE: Both Libsyn and Blubrry strongly suggest NOT using VBR for podcast episodes. Read what they say about it: Libsyn and Blubrry
4. The listener wrote, “However, you did misspeak at one point where you mentioned that stereo files are twice as big as mono files. …A joint stereo file might be just 30% larger than its mono counterpart, if there’s minimal stereo content…” I did some testing on Joint Stereo vs Mono file sizes and I’ve included my findings below. Please test this yourself and correct me if my findings are wrong.
FILE SIZE TEST – 60 Seconds of audio
Size comparison between file types and resolutions using Soundforge Pro 10.0 as well as Audacity 2.1.2. Each file contains the identical 60 seconds of audio.
- Stereo 16 bit, 44.1 kHz .WAV file = 10.0 MB (MONO = 5.04 MB)
- 128 Kbps Stereo MP3 (both Soundforge and Audacity) = 939 KB
- 128 Kbps Joint Stereo MP3 (Audacity) = 939 KB
- 128 Kbps Joint Stereo MP3 (Soundforge, Intensity encoding) = 939 KB
- 128 Kbps Joint Stereo MP3 (Soundforge, Mid-Side encoding) = 939 KB
- 64 Kbps Mono MP3 (Soundforge) = 470 KB
What are your thoughts?
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