Re: Sony FX1 (or Z1U)??

In article <TYOdnUNG848qqrLeRVn-uA@xxxxxxxxxxx>, Ty Ford <tyreeford@xxxxxxxxxxx> writes 
On Mon, 19 Sep 2005 14:26:21 -0400, Moving Vision wrote
(in article <lSuiwHKNLwLDFwKt@xxxxxxxxxxxxxxxxxxxxxxxx>):

As for the MPEG 2 audio the key is to digitise it into the system as 48K
PCM before doing anything with it. Once it's PCM you can muck about with
it 'till the cow come home and it won't be subject to further
compression issues.


Until you make a new DVD master and then you do what?    .....Oh, right,
compress the audio you have already reduced by 75% again. So what's left is
25% of 25%.

The first generation MPEG 2 recorded to tape on such 
as the Z1 is quite good enough for most purposes and actually better
then most other compact DV's because of the broadcast standard preamps.


Whose broadcast standard preamps? I'm feeding from a Sound Devices 442. You
use the preamps on the cameras????

Guess what. Go for it. However, I won't let you or anyone else go on about it
in ignorance.

Ty Ford



-- Ty Ford's equipment reviews, audio samples, rates and other audiocentric
stuff are at www.tyford.com



If anyone really wants to get into the issues relating to compressed HDV audio I'd suggest going to the site that Mike Kujbida posted earlier;


http://www.sundancemediagroup.com/articles/HDV_Audio_comparisons.ht

It's a very thorough and scientific article, with various wave form charts that pretty much covers the issues. As far as removing 75% of the data and then removing it again is concerned, well it doesn't really work quite as badly as that assertion might indicate. The 'missing' data is not really equivalent to losing 75% of sound itself, it's a codec that cleverly reduces the to the most essential bits of data. Once the first generation of compressed sound is converted to uncompressed PCM it is a complete sound recording, whether one feels its good enough or not is subjective but look at all the other MPEG offerings such as MP3, DVD and MD.

In your scenario you suggest that when the audio is recompressed back to DVD it's the same as throwing away 75% of the bit data twice, well I don't even think you believe that, you're just trying to be sensational in order to support your now well know opinion on the subject.

But for those who can't be bothered to go to the web site linked above, here's a few shamelessly copied paragraphs from the article written by Douglas Spotted Eagle/VASST Instructor ;

HDV audio is based around a somewhat new audio compression spec known as MPEG 1, Layer II. The bitrate is 384Kpbs. There are those that dislike this compression format; others that have no issue with it. The crux of the issue from the negative side, is that some audio professionals feel that compressed audio is bad. On the other hand, many audio pro's would suggest that compression isn't bad, it's just not as good as PCM/linear audio. (uncompressed)
The differences that need to be examined are:
1. What can the ear hear different, if anything, in a compressed audio format.
2. How well can the compressed format be processed in an NLE or DAW?
Another statement to consider is the sometimes-heard reseller hype that HDV audio is CD quality.
It's not.
This doesn't mean HDV audio is bad, It just means that it's not optimal when compared to PCM audio. PCM audio comes in various flavors of "good" as well. Is it 12bit, 22KHz audio? Or on the other side of the question, is it 24 bit, 192KHz? (no camera records this format)

This very brief examination was inspired by postings found on the web, suggesting that HDV-based productions should "double-record" audio to an MD player. If it's not an HDMD player, this suggestion is simply absurd, as you can easily surmise from the images below. Recording to a device like an Edirol R4, an HDMD player in PCM mode, a DAT machine, or other linear audio device is obviously of a higher quality, but also of a bigger production load and another button to push. (In the case of the Edirol, the LANC controller on HDV cameras will start/stop the unit along with the camera)

However, for general purpose/dialog audio, HDV audio has proven to be perfectly acceptable for both big screen and broadcast use. Below are images of a test performed using Mackie 626 speakers playing back a popular and fairly common rock tune. (Dire Straights "I Want My MTV) The audio is recorded from a mixer feeding an HDMD device recording in PCM, and the same audio signal split to the HDV-Z1U HDV camera going into the balanced inputs. The split was accomplished using a pair of Radial J3 splitters. (Jensen transformers inside, for optimal quality) The same recording was done using the line in of an Aiwa MD player recording with the ATRACS compression scheme, split off a bus on the mix desk. This was done as many people have recommended using an MD player to record with and I wanted to demonstrate the reason this is a very bad idea when compared to HDV audio. Not only is the HDV audio superior, but also doesn't require another device, and another button to push.

HDV audio is far from perfect. Frankly, so is linear, PCM based audio if you're using a DV camcorder to capture the audio. However, for dialog purposes, HDV audio is not only perfectly acceptable, it's preferable when considering the need for carrying double audio recording gear. If you were recording a John Prine concert, or a symphony, I'd definitely carry a DAT machine or other high end recording equipment such as the Edirol R4 device. And I'd suggest the same if you were recording these sorts of events on a DV camcorder too. Double record if audio range is critical. However, do not be concerned about the quality of HDV audio based on anti-HDV commentary found on various websites. These charts, and your own ears, bear out the quality of HDV audio and where it is quite useful and amenable to audio production.
Ironically, while listener acumen isn't a test of "what's good enough," most people are very happy with their 128Kpbs MP3 files on their personal music devices, and virtually no one ever negatively comments on AC3 audio, which is generally somewhat poor. Granted, these are delivery codecs, not acquisition codecs, but the quality of the HDV audio format is substantially higher than either of these delivery formats.

Keep in mind that the analog to digital conversion process is substantially more critical than the medium on which it is recorded. HDV camcorders, particularly the Sony Z1 and A1 camcorders, have outstanding converters. To get a better conversion, you'd need to step to an external box such as an EchoFire box from Echo, an Apogee Rosetta (if you've got serious cash) or one of the many M-Audio devices available.

Avoid recording to MD; you can clearly see that even the frequency range of spoken word is dramatically impacted. Using an iRiver device is another great option provided you're recording in PCM mode vs MP3 format.

Although converting the MPEG 1, Layer II stream into PCM audio at point of capture doesn't reconstitute the frequencies that were compressed, immediate conversion allows the file to maintain integrity throughout the editing process. Reverbs, delays, etc will be smooth and clean, once converted. Compressed audio formats shouldn't be filtered, as the recompression for final output may have issues. Most NLE's will convert the compressed audio to uncompressed when the audio is brought to the timeline, or converted to PCM when an intermediary format is introduced to the HDV video.

Record your HDV audio at appropriate levels; this will make the biggest difference of all when shooting with HDV audio. Use good microphones, just like you'd do with any other recording device, and get it close to the source. Make sure all gain stages are proper, so that you're recording clean, with robust levels, and you'll have no issues with compressed audio at all. This holds true for any audio that is to be compressed at any level, and for audio that isn't to be compressed. Good audio techniques are important regardless of the recording format.

Test your HDV camcorder to know how it will handle audio in a variety of shooting situations. You don't want to find yourself being quite knowledgeable about the visual aspects of the camera and ignorant of the audio aspects, do you? Sound is 70% of picture; it should encompass a substantial bit of your camera knowledge as well. Good sound is the absence of bad sound; great sound is pre-planned good sound.
Make your audio great.

Happy recording,

Douglas Spotted Eagle/VASST Instructor
--
John Lubran
.

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