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Author Topic: Why record at 24/48 versus 24/44.1?  (Read 19579 times)

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Offline boojum

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Re: Why record at 24/48 versus 24/44.1?
« Reply #15 on: July 31, 2009, 12:26:09 PM »
David, thank you for laying this out in clear and succinct detail.  I am on another board which is mostly pro, GS, and many if not most of the folks there doing studio work say they do it at 44.1.  I have suspected there would be losses in resampling which would offset any gains from sampling at the higher rates and that this was why studio work was being done at 44.1.  And because I believe I can learn more from someone who is in the business of getting paid for good recordings than from someone who dabbles in recording as a hobby I have followed what the pros indicate is best practice.  As a result I do everything at 24/44.1.  Had this not come up here with your lucid explanations I would have said nothing as it is so popular here to oversample that it is almost heresy not to.

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Offline notlance

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Re: Why record at 24/48 versus 24/44.1?
« Reply #16 on: July 31, 2009, 12:56:34 PM »
"Hi, my name is Paul, and I sample at 44.1 kHz."

I feel much better now.

This whole discussion takes on an "angels on the head of a pin" quality.  There are much bigger problems in recording such as where do I place the mic, the loud A/C in the room, the buzzing EXIT sign, the jerk that keeps thumping the mic stand, or ....  The only benefit of discussing 44.1 vs 48 is understanding why it does not make much difference.

If you are trying to make a living at this, the rule seems to be 44.1 for the music business, 48 for video/film.

Offline datbrad

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Re: Why record at 24/48 versus 24/44.1?
« Reply #17 on: July 31, 2009, 04:16:04 PM »
If the final delivery medium goal is limited to Redbook CD standard, and never will there ever be a need or desire to create a DVD (audio or video disc) to take advantage of the higher rates offered by those formats, or listen to the higher resolution files on a media server at better than CD sampling rates, then I agree that there is no reason to record beyond 44.1.

Problem is, many industry observers feel that in 10 years, physical media like CDs are likely going to be considered a quaint relic, and wave files on media servers will be the norm. So when that time comes, instead of listening to your now 10 year old recordings at 24/48 or 24/96, you will only have a 24/44.1 in your archive.
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Offline MSTaper

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Re: Why record at 24/48 versus 24/44.1?
« Reply #18 on: July 31, 2009, 05:34:44 PM »
While I completely understand the explanations and will likely go 24/44.1 when I tape tonight, I have to ask, if this is the norm, why have recorders that record 24/96 or even 24/192? In what situations would this higher sample rate be beneficial? Commercial video applications?

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Offline Mike R.

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Re: Why record at 24/48 versus 24/44.1?
« Reply #19 on: July 31, 2009, 06:03:17 PM »
While I completely understand the explanations and will likely go 24/44.1 when I tape tonight, I have to ask, if this is the norm, why have recorders that record 24/96 or even 24/192? In what situations would this higher sample rate be beneficial? Commercial video applications?

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Offline BC

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Re: Why record at 24/48 versus 24/44.1?
« Reply #20 on: July 31, 2009, 06:40:44 PM »
While I completely understand the explanations and will likely go 24/44.1 when I tape tonight, I have to ask, if this is the norm, why have recorders that record 24/96 or even 24/192? In what situations would this higher sample rate be beneficial? Commercial video applications?

MSTaper

I would think high res sampling could be beneficial in a recording situation with excellent acoustics (I'm thinking pro recording session in a studio, concert hall and the like), as opposed to a concert in a noisy bar or ampitheater. There are some classical studios allowing you to download 24/96 or even 24/192 studio-master quality files these days.


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Offline DSatz

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Re: Why record at 24/48 versus 24/44.1?
« Reply #21 on: July 31, 2009, 07:16:23 PM »
Jesse Hurlburt, I was referring to the possibility that the anti-aliasing and -imaging filters in a (say) 96-kHz recording system might have lower group delay at (say) 10 kHz and above than the corresponding filters in a 44.1 kHz system. Filters are an inescapable part of any digital audio recording system, and a higher sampling frequency allows them to be better and/or to affect the audible portion of a signal less.

But the relative importance of this as compared with, say, room acoustics and microphone placement shouldn't be overstated. It generally takes special test signals to be able to hear the advantages of the better filtering, and special playback systems besides--loudspeakers generally have horrible phase and distortion problems at the highest audio frequencies, so most often electrostatic headphones have to be used if the difference is to be detectable at all--and even then, most listeners hear no difference, since our ears are rather insensitive to phase distortion at such high frequencies. So we are really talking about a subtlety, although I have every respect for those who wish to preserve such subtleties.

As far as I'm concerned the filtering advantage is the only possible audible advantage of a high sampling rate (i.e. higher than "2 x 20 kHz plus a little") even though in practice, it is far more of a measurable than an audible phenomenon. Preserving frequencies higher than we can hear certainly doesn't benefit the frequencies that we can hear; that's been investigated every few years since at least the 1930s and the results have always been either negative or non-reproducible. And the whole notion that a higher sampling rate "fills in the space between the dots better" is just ... sad (and more to the point, incorrect).

--best regards
« Last Edit: July 31, 2009, 08:26:13 PM by DSatz »
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Offline Will_S

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Re: Why record at 24/48 versus 24/44.1?
« Reply #22 on: July 31, 2009, 08:11:43 PM »
While I completely understand the explanations and will likely go 24/44.1 when I tape tonight, I have to ask, if this is the norm, why have recorders that record 24/96 or even 24/192? In what situations would this higher sample rate be beneficial? Commercial video applications?

MSTaper

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Mainly that.  But as DSatz mentions, potentially some theoretical advantages that are unlikely to be heard in practice, but why not do it if you have the space.

Also, higher sampling rates are indisputably handy if you want to record bats. For real, I know a several field biologists who need to be able to record frequencies well over 20kHz, although of course they can't hear the ultrasonic part of the signal without processing it first.

Offline DSatz

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Re: Why record at 24/48 versus 24/44.1?
« Reply #23 on: August 01, 2009, 10:04:06 AM »
BC, you wrote:

> I would think high res sampling could be beneficial in a recording situation with excellent acoustics (I'm thinking pro recording session in a studio, concert hall and the like), as opposed to a concert in a noisy bar or ampitheater.

Well, "resolution" isn't really a term with a single, agreed-upon meaning in audio, and here I think that you may be confusing sampling rate with bit depth (the number of active bits per sample). The number of active bits per sample determines the dynamic range capability of a recording system. The best available A/D converters at present have a little over 21 bits of resolution under ideal conditions, so their output data is generally stored in 24-bit samples.

The reality of all live recording--even in a very quiet studio--is that there is always an acoustical "noise floor" and an electrical "noise floor," and there is also a maximum sound pressure level; the dynamic range of the recording is what falls in between these two limits. During the heyday of the vinyl LP a 65 to 70 dB dynamic range was considered outstanding; that is about equivalent to only 11 or 12 bits. The earliest commercially available professional "16-bit" digital audio recording systems had only 14 bits of active data per sample, which already blew any analog tape recorder out of the water, even with advanced noise reduction and high-output tape.

What I'm getting at is that very, very few live recordings fully utilize a 16-bit dynamic range, which is absolutely enormous. When 24-bit recording was introduced, the rationale was that it was strictly for high-end professional use so that a 16-bit range could be maintained throughout a complex studio production, e.g. multi-track mixdown and signal processing, which would all occur at 24 bit resolution until the final mix which would be 16-bit.

That's about as far as the influence of rational, engineering-driven planning went. Everything else after that was the market in action. I can sell my toy better if it has this or that specification which is a "professional" specification--and if it uses 24 bits to convey (say) samples that are really only accurate to 15 bits, then I can still peddle it as a 24-bit recording device, and someone will buy it, take it home and congratulate himself on having it.

People like us use 24-bit recording for security--we can set our record levels a little low, not worry about the peaks, then normalize the levels when we dither down to 16, making ourselves look like level-setting geniuses. And for certain laboratory uses, or systems which drive the loudspeakers to extremely high SPLs, a wider dynamic range can be important. But the range between the noise floor of people's domestic playback environments and the loudest that their playback systems can reproduce is generally quite a bit (so to speak) less than a 16-bit range.

Meanwhile the entire mass market has gone diametrically away from high quality audio in favor of portability. I don't personally limit myself to recording at the audio quality level of an mp3, or the incredibly bad sound of most radio stations, or videos on the Internet, but I do have to notice that about 98% of what people listen to these days is that.
« Last Edit: August 01, 2009, 12:28:35 PM by DSatz »
music > microphones > a recorder of some sort

Offline Chuck

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Re: Why record at 24/48 versus 24/44.1?
« Reply #24 on: August 01, 2009, 11:53:09 AM »
Yeah, this is the raw, blunt truth of digital recording. Thank you, DSatz, for stating it so well in easy to understand language.

44.1kHz, 16 bit, stereo, PCM (CD quality) audio was engineered to deliver full bandwidth and dynamic range of recorded music for humans to enjoy.

I think there is plenty of room to debate the stereo aspect of the CD spec, because two channels only approximates a 3-D sound field. But, the bit rate and sample rate cover all of the measureable aspects of audio reproduction.
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Offline notlance

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Re: Why record at 24/48 versus 24/44.1?
« Reply #25 on: August 01, 2009, 12:38:48 PM »
Problem is, many industry observers feel that in 10 years, physical media like CDs are likely going to be considered a quaint relic, and wave files on media servers will be the norm. So when that time comes, instead of listening to your now 10 year old recordings at 24/48 or 24/96, you will only have a 24/44.1 in your archive.

I agree that CDs will become quaint in a few years; a few years after that midia servers will be also obsolete.  Nevertheless, I'll be happy to listen to my 44.1 kHz files because a properly converted 44.1 kHz file contains ALL the information contained in a 20 Hz - 20 kHz analog signal.  If a 44.1 kHz sample has ALL the information, then a 48 kHz, 96 kHz, 192 kHz, or infinite kHz sample cannot have more information.

Notice I said a properly converted sample.  There certainly are problems that can arise during the A/D process.  However, if my recorder has audible problems converting at 44.1 kHz, I don't think all those problems will suddenly disappear if I set it to sample at 48 kHz or higher.  Fortunately, my recorder seems to do fine at 44.1 kHz, so that's where I leave it.

I have had clients that insist on 96 kHz.  In that case I don't argue sampling theory with them; I pull up the sampling rate menu item and set it to 96 kHz.  I do find it interesting when they are happy to accept a CD copy of the final mix.
« Last Edit: August 01, 2009, 12:46:06 PM by notlance »

Offline DSatz

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Re: Why record at 24/48 versus 24/44.1?
« Reply #26 on: August 01, 2009, 12:53:05 PM »
Um, at the risk of seeming like (or actually being) a blabbermouth/know-it-all...

Chuck wrote:

> 44.1kHz, 16 bit, stereo, PCM (CD quality) audio was engineered to deliver full bandwidth and dynamic range of recorded music for humans to enjoy.

Well, the truth is that when these parameters were chosen, they were slightly beyond the reach of commonly available technology; then as professional PCM recorders and the digital audio CD were brought into production and use, they were achieved first tentatively, and then more definitely. The technology has progressed considerably further since then, and if today's technology could have been available then, we can't know whether the same decisions would have been made. In some ways I kind of doubt it.

This was years before DAT or DASH recorders were invented, so for Sony (and later JVC), the natural recording medium to accompany their PCM audio processors was segmented video: 3/4" U-Matic or in some cases, the industrial versions of the 1/2" Beta and VHS formats. Thus the choice of sampling rate was tied by design to the field rates of the PAL and NTSC video systems. It was also limited by the available A/D converters of that time, which imposed a tradeoff: The higher the sampling rate, the more noise and distortion they caused. As it was, those converters had to be adjusted carefully for lowest noise at each recording session (part of how I made my living in the early-to-mid 1980s).

Those were requirements imposed by the need to sell a complete package to the studios, record labels and other recording clients. The late Dr. Thomas Stockham's "Soundstream" system, on the other hand, used computer data recorders and was thus free to use a somewhat higher sampling rate (50 kHz) and correspondingly simpler, better-sounding filters. Shannon's Sampling Theorem states that any sampling rate is adequate (and thus, equally good) as long as it is more than twice the highest frequency present in the signal--but it doesn't deal at all with the problems of limiting the signal to that frequency range.

Since those problems are most severe when a filter has to cut off very sharply, I can well understand the wish for somewhat higher sampling rates, now that converters and recorders are available to handle them, and now that the characteristics of video recorders aren't a factor any more. For example, 64 kHz would give enough of a margin that the filters wouldn't need to be very steep.

But I fear that nothing will ever satisfy the people who basically don't understand how digital audio works, and who therefore keep ASSuming that higher and higher sampling rates will bring about a closer and closer approximation to the input signal.
« Last Edit: August 02, 2009, 01:43:52 PM by DSatz »
music > microphones > a recorder of some sort

Offline Chuck

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Re: Why record at 24/48 versus 24/44.1?
« Reply #27 on: August 01, 2009, 12:59:13 PM »
Thanks for the clarification. As always, DSatz, you are a wealth of accurate information on this stuff...  ;)
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Offline darby

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Re: Why record at 24/48 versus 24/44.1?
« Reply #28 on: August 02, 2009, 04:37:31 PM »
I merely tape shows as a hobby and unfortunately have no real formal training, or professional experience
so in light of the last few posts would someone care to explain the significance (or insignificance) of this chart:
it appears to me the higher the bandwidth, the closer to realistic it is

Offline DSatz

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Re: Why record at 24/48 versus 24/44.1?
« Reply #29 on: August 02, 2009, 07:42:05 PM »
A Dirac pulse is a theoretical signal that has infinite bandwidth, but human hearing is real and doesn't. The filters that these impulses are being put through certainly don't, because they're filters--their whole purpose is to limit signal bandwidth. And band-limited systems can't have perfect impulse response.

But listening tests have shown that a recording system doesn't need perfect impulse response in order to be audibly transparent; rather, there are thresholds of group delay at various frequencies beyond which no further audible improvement occurs when group delay is reduced further.

For decades people gladly tolerated the dreadful impulse and phase response of vinyl LPs and analog tape--yet when digital comes along, which is light years better where it counts (between/among channels), they all of a sudden grow virgin bat ears and become allergic? I don't buy it.

That understood, let me raise the "counter-question" of how different those scope traces would look from one another (if that's what they really are, rather than MatLab graphs as I suspect) if they were band-limited to the human hearing range? That would be the first clue to whether any audible differences could possibly be present or not.

But those impulse drawings can only help answer that question if you know the time scale of the impulses, so that you can infer their spectral content. Omitting an explicit time scale from an illustration of this kind is a major lapse of fairness. Another thing I'm sorry to see is the so-called "analog system"--the only thing with impulse response anything like that would be a short length of "analog" wire. Even 30 ips tape is nowhere near that clean.

--best regards
« Last Edit: August 03, 2009, 08:38:33 AM by DSatz »
music > microphones > a recorder of some sort

 

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