Topic: Dithering and mixdown to 44.1 from 48kHz - why not just record in 44.1?

[acidjack]

I am assuming I already know the answer to this, but I'd like to hear some scientific explanation if possible. 

A lot of people record in 24/48 or 24/96 and then seem to dither to 44.1 when they release to the public.  Obviously to do that, your software has to engage in dithering, which causes at least some theoretical quality loss from both the process and, of course, the loss of bits.

It seems to me, especially if you aren't one of the people who mixes down to multiple formats, aren't you better off just recording in 44.1 to start with?  Or do you really plan to go back one day and re-mix it down to get back those extra 3.9bits? 

Has anyone ever tried to do some kind of a controlled test to see whether a 48kHz recording sounded audibly different than a dithered 44.1? 

[matahaka]

I believe.. you can refer to this thread..

http://taperssection.com/index.php?topic=125051.msg1662541#msg1662541

[Shadow_7]

I tend to record at or above 24/96 because I generally have two outputs.  Audio only CD(44.1kHz) and Video with audio (48kHz).  Having the higher rate allows better odds of getting a good end result in BOTH.

I'm not sure on the science of it, or even the technicals(yet), but the kHz is the resolution(samples per second).  You can't take an SD video and make a great HD video from it.  With extra bits in audio, you're at worst throwing out half the samples.  At best perhaps time shifting some samples that byte or two to have a more detailed result at the lower kHz.  Which if captured digitally at the lower kHz would only give you one or the other or let them do battle without any hope of arbitration.

I mainly do the higher kHz, so I can EQ, and other harsh edits to the source BEFORE down sampling.  Which, if only in my mind, yields superior results.  In theory mics lose some of the high end over time.  And other less than perfect mics to start with.  So IMO, having the higher starting point allows you to do more processing in post without the ill effects.  Or at least less of them. 

If I had to choose between just 44.1kHz and 48kHz, and only those two, it would probably depend on the project at hand.  Whatever end result paid the bills would be the one to win.  Or depending on the content being recorded.  No qualms from me about recording lectures and other non-musical things at 44.1kHz for video.  Even with DSD capability at my fingertips.

[page]

I'm not sure on the science of it, or even the technicals(yet), but the kHz is the resolution(samples per second).  You can't take an SD video and make a great HD video from it.  With extra bits in audio, you're at worst throwing out half the samples.  At best perhaps time shifting some samples that byte or two to have a more detailed result at the lower kHz.  Which if captured digitally at the lower kHz would only give you one or the other or let them do battle without any hope of arbitration.

I think you might be confusing video sampling/display and nyquist sampling. In video, you have X amount of visual space, and HD video gets crammed into that space where SD video gets spread out so more details renders a sharper picture when viewed on the same tv. In nyquist, you get 2 samples for each frequency per second regardless of whether you sample at 44, 48, or 96. You still only get 2 samples at 600hz. What you get with 96 vs 48 is the ability to (presuming your speakers can render that information) torment your dog with information in the 30khz band where as thats gone at 48 sampling. What's particularly amusing or infuriating (depending on your objective is if you have equipment or an environment that has a hum/buzz in those upper echelons (I once had a mic that did regardless of what where I was recording).

To me, the last technical discussion of personal interest is whether your initial ADC chipset is better at the end result (e.g. 44.1 or 48) than your software resampling algorithm that you're using. As the folks at Sound Devices once said: "recording at 192khz is great for sound effects generation, not effective for recording a PA..." If your algorithm introduces noise elsewhere in the audio band, than it's sort of self-defeating to sample higher then that for a non-time-shifted function (e.g. slowing down information for special effects creation), and I find it somewhat surprising how many algorithms do. Someone did a bunch of graphs on the subject and you get a visual representation of low level noise "smear" depending on what you chose to compare. Neat stuff.

[notlance]

A lot of people record in 24/48 or 24/96 and then seem to dither to 44.1 when they release to the public.

Just to keep this discussion a little less confusing, let's define the words.

A simple but by no means complete definition of dither is the process of adding noise to a signal before A/D conversion in order to reduce distortion due to quantization error.

Converting a signal sampled at 48 kHz to a 44.1 kHz signal is called resampling or sample rate conversion, and that is the process you are describing.

[notlance]

Has anyone ever tried to do some kind of a controlled test to see whether a 48kHz recording sounded audibly different than a dithered 44.1?

Here is one controlled test:

http://drewdaniels.com/audible.pdf

[Lil Kim Jong-Il]

If you plan to circulate your recordings on CD or DVDA, then you you can record at 44.1 and put the tracks directly to disk.  If you want to use your recording as an LPCM track on a video DVD, the spec allows only a 48k or 96k sample rate.  There was a time, and it may or may not still be the case, that a lot of consumer DVD players don't handle DVDA discs.  So when I put my 24-bit stuff to optical media to play at someones house, I author as a video DVD with 24-bit LPCM track.  Sampling rates other than 48K and 96K won't work for that and I don't see the point of converting from 44.1k (or 88k) to 48k.  There are no issues on any file based players with 48k so it's only for CDDA disks that 44.1k is of any interest. 

[Shadow_7]

A lot of people record in 24/48 or 24/96 and then seem to dither to 44.1 when they release to the public.

Just to keep this discussion a little less confusing, let's define the words.

A simple but by no means complete definition of dither is the process of adding noise to a signal before A/D conversion in order to reduce distortion due to quantization error.

Converting a signal sampled at 48 kHz to a 44.1 kHz signal is called resampling or sample rate conversion, and that is the process you are describing.

But with a lot of software you get to chose the type of dither when you resample.  So it's not as simple as just saying dither or resample, you can't have one without the other.  Whether it's 96kHz to 44.1kHz or 48kHz to 44.1kHz OR just adding EQ.

And then there are those frequencies beyond the sampling resolution that will get sampled at half their frequency, if you don't use a higher sampling rate.  i.e. 30kHz (beyond human hearing) recorded at 15kHz (within the range of human hearing).  And some mics are very sensitive well into and past that frequency.  And many things will produce those frequencies.  Maybe not your speakers, but they'll try.  At the higher sampling rates, you have a better chance of filtering those off.  i.e. less overall noise.

[goodcooker]

I record at 44.1 kHz sampling rate since I can't hear a difference at higher rates and scientifically the sample rate divided by two is the top end of the frequency range of the recording. Half of 44.1 is 22.5 kHz and I can't hear over 17.5 kHz so I don't see the point.

I think artifacts introduced by the resampling process (depending on your software/process, I use Wavelab) are more likely to do damage to your recording than just recording at the lower sampling rate.

[page]

But with a lot of software you get to chose the type of dither when you resample.  So it's not as simple as just saying dither or resample, you can't have one without the other.  Whether it's 96kHz to 44.1kHz or 48kHz to 44.1kHz OR just adding EQ.

Sure you can, I can dither something and not resample it, likewise I can resample something and truncate it without dither. Second, I can think of a couple of software packages, both free and expensive, that have the two segregated so you control when they occur independantly.

And then there are those frequencies beyond the sampling resolution that will get sampled at half their frequency, if you don't use a higher sampling rate.  i.e. 30kHz (beyond human hearing) recorded at 15kHz (within the range of human hearing).  And some mics are very sensitive well into and past that frequency.  And many things will produce those frequencies.  Maybe not your speakers, but they'll try.  At the higher sampling rates, you have a better chance of filtering those off.  i.e. less overall noise.

I'm assuming you are referring to harmonics, because I can't think of anything else at 30khz that I'd want to reproduce verbatim in a music recording without altering the speed, and whatever is coming across to be sampled at 15khz is still there regardless of whether I chose 48k or 96k. Actually, I can't think of anything I'd want to reproduce verbatim at 30khz period.

1) Just because there is information there, and you're speakers try to resolve it and fail, doesn't make it positive. Gallant attempting and failing is still failure.
2) As DSatz, my audiologist, and others have pointed out; humans exposed to concert environments can't really hear much past around 17khz anyway. So recording anything up there is sort of moot for our purposes. Which brings me to #3:
3) Whether you filter something when you have 48khz of information or 22khz of information at the time of recording is moot if at the end of the day your target audience can't hear it, and you're chucking it anyway.

So I'm with cooker et al; I think you're more likely to do damage through the adding of artifacts and distortion to your recording via resampling if you have a bad algorithm rather than recording at a lower sampling rate.

Has anyone ever tried to do some kind of a controlled test to see whether a 48kHz recording sounded audibly different than a dithered 44.1?

Here is one controlled test:

http://drewdaniels.com/audible.pdf

neat read.

[Lil Kim Jong-Il]

But with a lot of software you get to chose the type of dither when you resample.  So it's not as simple as just saying dither or resample, you can't have one without the other.  Whether it's 96kHz to 44.1kHz or 48kHz to 44.1kHz OR just adding EQ.

EQ is also independent of dither.  Digital EQ may add some noise as a result of it's calculations but that is not the same as noise added by the dithering algorithm. 

[F.O.Bean]

I have read all there is to read about this situation, and I record at 24-Bit/44.1kHz!!! It makes putting it to disc easier and is still leagues better than recording in 16-Bit

[stevetoney]

Speaking for myself, it's been at least two years since I've used CDRs, so I stick with 24/48. 

FWIW, I just read somewhere that Sony is producing 20 million fewer CDRs daily than they were at their peak.

[ghellquist]

This is a matter that has been discussed and discussed on just about every forum talking about recording.

When thinking back, I believe most discussions ended up with the following arguments that sort of tend to boil up as concensus.

1) different equipment handles different max sample rates
2) some equipment does handle some of the possible sample rates rather badly ( one example might some of the Sound Blaster generations that only handled 48kHz natively, everything else was software resampled behind the scenes ). Even rather high-end equipment has been shown to support some of the sample rates less well the others to choose between.
4) higher sample rates means larger files and higher load on your computer ( which might be moot if you computer is fast enough and your hard drives large enough )
5) different end media may set restriction on what sample rates are allowed for your end result
6) best bet is for you to try your own equipment in your own application, from recording to end result at different sample rates. You might preferr one of them.

Nothing else seems to be a common consensus. Some like a high sample rate and resampling, others hate resampling, some say that resampling has to be at even divisors, others show scientifically that it is not so. And then there are two camps of people where one camp says that hearing ends at about 20kHz and the other camp says recordings has to go well above that to capture the full story and that we can hear that.  Add to that a lot of peole that, frankly speaking, really does not seem to have a clue either way, but still airs their opinions.

Now, for my own, rather humbling recording needs ( acoustic classical music ) I tend to record at 44.1kHz.
I did follow my own advice 6 above, and did some tests.

// Gunnar

[twatts (pants are so over-rated...)]

I record and listen with the best quality I can get.

I do the 16/44 thing for the Masses, so they can burn their CDRs. 

Terry