sample rate problem...

Special Interest Groups Audio Processing
1

Hi

I recorded a piano demo for a web video broadcast at 96000 24bit. Sound is excellent.

However, when merging with a video (replacing the video’s audio track with the audacity captured audio), the sound is compromised when played via a flash video player. As an .avi or mp4 - the audio is perfect. I have found that the highest sample rate for audio via a flash video player is 44100hz, 320kbps. This is high spec. and should therefore still sound great… but i then thought perhaps the video conversion (server side conversion) was working too hard taking a 96000hz to 44100, so I re-sampled in audacity and exported as an both an mp3, WAV 16bit and m4a (aac) with the audio parameters of the flash video players and immediately heard in audacity the same compromise as heard via a flash player.

The compromise is a faint ‘zing’ distortion over every note/sound. I don’t hear it when re-sampling in preview - but do once exported, and I do hear it in preview when I change the project sample rate.

As a test, I imported a recording that had not been captured on audacity and had worked out really well in flash video, and resampled and set the project rate to 44100hz. Same thing happened.

Is this a compression issue?

As this is a piano demo video - the sound quality is paramount - and 44100hz is industry standard right? - so it should be a very acceptable quality.

I really appreciate any help you can give on this.

2

44.1kHz 16bit PCM stereo is the industry Standard for CDs (the famous “Red Book”)
48kHz is the industry standard for DVD
The CD standard was chosen way back in the early 80’s as a compromise for very good sound (not the very best) and fittiing the whole of Beethoven’s 9th sumphony on just one CD. Serious archivists often use higer quality settings - but if you need something that will play on most kit the 44.1 16-bit is good

[quote=“willvenables”
The compromise is a faint ‘zing’ distortion over every note/sound. I don’t hear it when re-sampling in preview - but do once exported, and I do hear it in preview when I change the project sample rate…Is this a compression issue?[/quote]
Possibly it could be down to dither (deliberate noise which is added when downsampling - see: http://wiki.audacityteam.org/wiki/Dither ) but it could also be MP3 compression damage (unlikely at 320kbps)

I’m hoping that Steve Daulton will come by this thread - he knows a lot more about this than me :slight_smile:

WC

3

thanks waxcylinder -

thought I should add… i have fast sync interpolation set for real time conversion, and high quality interpol for high quality conversion - both are set to dither: none.

Also, when i change the project sample rate to 3200 - the noise goes.

4

Is that a typo?