Audio loss in video transfers?

[theair]

Hi again

I recently asked about some hi8 tapes of concert recordings -- I'd assumed the quality remained decent during the tape > DVD transfer process but as several pointed out, my assumptions were probably wrong :/

It did prompt me to wonder about something else :

It's clear that there are quantifiable measures when transferring/capturing video in the digital world - the resolution/dimensions/pixels/lux/chroma/etc - but very little (afaik) attention seems be given to anything dealing with audio. Obviously there are less traits with audio - but does audio suffer any (significant) loss in quality when going through conversions as well?

[dpalomaki]

Audio need not suffer quality loss and is generally not as picky as video transfer/conversion. The issues in conversion include setting levels to avoid clipping/distortion while staying above the noise floor of the system, channel balance for stereo recordings, and possible "sweetening" of the sound to address venue noise (e.g., HVAC blowers), room tonal balance, camcorder noises, and so on.

Video8/Hi8 had roughly FM radio level audio quality potential, although much Video8 was monophonic recording. The limiting factor with home video was generally the microphone setup used with the camcorder - the internal mics were generally poor and most recording venues were not conducive to quality sound recording. Not an issue for most kids birthday parties, the pits for musical performances.

The audio measures would include frequency response, distortion, and signal to noise/noise floor. Some of which are limited by the sample rate and bit depth in the digital domain as well as compression scheme used.

DVD's support both compressed and uncompressed audio, although compressed is perhaps more common. MediaInfo can give you the specs on the audio.

For audio your ears are the ultimate judge.

[theair]

Thanks -- My main reference points in regards to the audio degradation are from my tape trading days - when one would note 'generations'... There are many recordings out there that later needed to be pitch corrected due to the lack of quality control (different decks, dolby, etc.)...

I hope a bit more attention will be paid to internal microphones one day. It's swell to know that I can make a 4K movie on my phone (that literally has a 1TB capacity), but the fact that the internal mic has not improved AT ALL (and when any zooming in is done, the 'zoom audio' Feature is automatically enabled and sounds terrible) is pretty depressing.

[dpalomaki]

Pitch correction is an issue with analog audio tape; speed variations cause pitch changes. Because analog video tape is driven by precise crystal controlled clock speeds (frame rates) pitch change should less an issue.

Generation loss is an issue with analog tape and analog signals. Generation loss is not an issue for digital as long as there is no de/re-encoding involved. Audio in Video8/Hi8 is recorded as AFM on tape so the losses result from the demodulation/modulation of the FM signals recorded on tape, and should be less severe than would be the case with analog audio tape.

Camcorder built-in mics have improved over time, mainly seen in the better camcorders. But poor implementations still abound. Built-in mics dominate because Joe and Jane Sixpack are not about to hire a sound man and his system to accompany their back yard BBQ shoot.

Good microphones require physical space. Good audio recording requires using the proper type/design microphone(s) in appropriate locations relative to the sound source(s) of interest. A "zoom" microphone implies attempting to create a shotgun mic- like pattern. Doing that in a hand held cellphone is problematic. The higher end "prosumer" camcorders use better microphones and have better onboard mic placement but still not great for high quality audio. Most offer options to use of external mics which is the approach to take for best audio. But audio recording is a separate field and skill set.

[theair]

That makes sense in regards to the analog v digital, thanks for that explanation.

I mention the "audio zoom" as it's what everybody's favorite company (Apple/Mac/iphones) implements whenever shooting video and zooming in on anything; I've recorded a bit of live music with my iphone and it sounded OK until I zoomed in a bit and the sound got much worse...turns out this is due to this feature, which is impossible to disable. It's not easy to find much information about it...the fact that the word "zoom" is now mostly used for something else doesn't help.

[dpalomaki]

https://www.dxomark.com/what-is-audio-zoom-for-smartphones/

The old mid-side stereo recording technique is a related technology. FWIW: In the 1990s Canon offered a "zoom" stereo microphone (ZM-100) for its Hi8 camcorders. It believe it used mid-side capsules and zoomed by adjusting the mid-side mix rations.