Some fundamentals...

[realysm42]

Morning all,

I've read a lot of words being used here that I've not heard used before so I was wondering if you could proveide an explanation for a couple:

Up/Down/Re-sampling

24bit @192 (etc)

I understand the latter is something to do with the quality/resolution of what you're hearing and the above is what most people strive to hear. One question I have on this though is what's the benefit?

I've started using Foobar 2000 and it gives you data on what you're listening too, all of my cds are something like:

16 bit @ 44100 hz
Format: Lossless WAV

If that's the resolution of what the CD's recorded at, is there any point in me "upping the resolution" via my sound card?

For anyone that plays pc games, would it be similar to have a game at your native resolution but having antialisaing turned on (a post processing effect to enhance what is it you see)?

[Macca]

Morning to you too:D

Upsampling - taking a digital signal and artificially increasing the sampling rate by making an educated guiess as to what is mising - suposed to give benefits in lower distortion, instrumental timbre and sound staging

Downsampling - taking a digital signal and reducing the amount of data in it - e.g copying a CD to MP3 - it will probably not sound as good but the file will take up less space than the full resolution one.

Re-sampling - taking a chunk of signal and using it for something else - like nicking the hi-hat off or a bass riff off an old seventies funk record and using it in a modern rap recording, for instance.

Hope that helps:)

[bobbasrah]

Google is your friend here Martin
Up/down is all re-sampling, or converting the source digital signal to another format. Upsampling a CD to say 24 bit does not alter the content one bit (pun unintended) as you cannot add what is not there in the first place. Downsampling, is the exact opposite where you chop bits off,
16bit 44.1kHz is the standard (Redbook) format for CD.
24/96 is what used to be used in studios, for later re/down-sampling to 16/44.1 for the CD for sale.
A 24/96 is not necessarily higher quality, but can be depending on how it is mastered. I have stunning 24/96 and stunning 16/44.1, and most of the 24/96 sound better than the original CD issue, which is why I got them. The CD issued was crap because of mastering or how the label dictated it should sound.
You can read on one of the threads (I think F1Eng?) who made the point that each issue is generally mastered in the studio to suit for the same album - LP/CD/SACD/etc..
To bugger things up good and proper, the way the hardware deals with that digital signal to make it analogue can be better suited to a particular standard.
Plenty on the net for further info...

[realysm42]

Cheers guys.

It's interesting you say that Bob, because I'm pretty sure that I read (on this forum somewhere) someone said that they try to avoid playing something than the original bit rate for music to avoid up-sampling atrefacts.

They might be talking out of the arse of course, what say you?

(I think by yout logic, it doesn't matter if you play a 44 file at 192, it doesn't change the sound atall)

If that's the case, isn't it over kill having all of these incredibly high bit rates that 99% of studios don't record at?

[bobbasrah]

Cheers guys.

It's interesting you say that Bob, because I'm pretty sure that I read (on this forum somewhere) someone said that they try to avoid playing something than the original bit rate for music to avoid up-sampling atrefacts.

They might be talking out of the arse of course, what say you?

(I think by yout logic, it doesn't matter if you play a 44 file at 192, it doesn't change the sound atall)

If that's the case, isn't it over kill having all of these incredibly high bit rates that 99% of studios don't record at?

The first comment is possible, but I have heard no improvement in upsampling, despite some who claim it does. The latter I suspect is because their conversion is better suited to their DAC at the higher rate, as it is cannot be adding anything to the original. I used to speak out of my arse too, then I left the Civil Service. Been uncivil ever since, other than in engineering. :doh:
The studio bitrate I think allows a degree of latitude in how they do the transfer to CD, but I'm not sure.

I say again, a good quality sample is what you are after, but some are good some are bad. I have get to hear a bad 24/96, but perhaps that is down to better mastering.:mental:

[Macca]

The first comment is possible, but I have heard no improvement in upsampling, despite some who claim it does. :

I wouldn't necessarily use the word 'improvment' but upsampled does sound 'different'. Some may prefer it. I have a Cambridge CDP that upsamplings everything to 24/196 but usually I prefer the presentation of my old Bitstream Sony.

[sq225917]

Upsampling: interpolating new sample values between existing values to increase the number of samples per second. ie taking A-C-E-G and coming up with ABCDEFG.

Downsampling: the opposite of upsampling, reducing the number of data points per second. (Not to be confused with data reduction, as has been done above by Macca who is more closely describing lossy compression via transcoding).

While you cannot realistically make up info that simply wasn't there to start with, increasing the samples per second, upsampling, does allow the dac chip to run 'softer' filters to remove the products of aliasing, the higher the data rate the fruther above your 20khz hearing limit these exist, potentially removing some audible effects of 'fold back' from the filters.

Basically don't worry about it, play your music in it's native data rate and format.

[Macca]

.

Downsampling: the opposite of upsampling, reducing the number of data points per second. (Not to be confused with data reduction, as has been done above by Macca who is more closely describing lossy compression via transcoding).

.

True:doh:

[bobbasrah]

And I was about to query the 196 upsample....
When all is said and done, whether it be filtering or other implementation, some gear does seem to respond better to different digital signals, which of course throws the whole argument of the old digital debate into turmoil with so many other variables.
However, I remain convinced that many of the 24 bit albums I have were better mastered than their CD counterparts, perhaps for the SACD or DVDA markets.
I also have some cracking 16bit tracks (downloaded) which are stunning in range and dynamics I rarely heard from many CD's, again probably due to mastering.

[Welder]

This is an excellent site if you're a bit hazy about file/computer based audio.

http://thewelltemperedcomputer.com/

[realysm42]

Cheers chaps :)

[dave2010]

The sampling theorem suggests that upsampling will not give any benefits.
Upsampling is when the sample rate is changed to one higher than the original recording.
Downsampling is when the sample rate is changed to one lower than the original recording.

Upsampling/downsampling by factors of 2 is relatively straightforward. Thus 48kHz->96kHz and vice-versa are fairly easy and usually only introduce minimal artifacts.

Usampling/downsampling by other factors may introduce measurable artifacts - e.g 44.1kHz -> 96kHz is not a factor of 2, so there could be moderately significant artifacts.

Downsampling will reduce the range of frequencies which can be reproduced, and may also introduce aliasing in which high frequency sounds are folded back to produce audible, and possibly disturbing sounds.

Downsampling should normally be done with an anti-aliasing filter, to remove high frequencies which can cause this problem.

A lot of digital signal processing now uses both up and down sampling, and digital filters in order to achieve desired effects. Digital filters are generally much more accurate than analogue ones. Some CD and DVD players deliberately upsample to very high sampling frequencies, then do some digital processing before downsampling back into the audible (or visible for DVDs) ranges. For various reasons this can give improved results.

One of the basic principles is noise shaping, in which noise which might be in the signal is moved to a much higher frequency, where it might not do any harm (i.e you can't hear it or see it) or can be removed.

Interpolation is also part of the process, and it is conceivable that if done well this can result in smoother sound. Most interpolation is done independently of the signal (using linear processing), but some techniques might change the interpolation depending on the data (non-linear processing), and this could give perceptually better results. This is perhaps more common in image processing.

One problem might be that further digital processing can cause problems with encoded digital data, if noise which has been moved out of range is then subsequently (usually inadvertently) processed and more artifacts can then appear. This is something that BBC engineers found with early DAB broadcasts when broadcasting compressed digital audio.

Whether there is any real merit in upsampling may depend on the equipment used. As has been mentioned, it is possible to get good results with standard (44.1kHz) rates for CD even with only 16 bit resolution, as well as some recordings at higher resolution and higher sample rates e.g 24 bit 192 kHz.

It is possible to make lousy recordings at all resolutions and sample rates!

[realysm42]

I hear you; thanks for the comprehensive answer.

It's odd to come from a gaming background to hear phrases like interpolation and anti-aliasing in other areas.

Have you any experience with dithering? Could this be described almost as random interpolation?

I understand how it might help on some recordings, would it be to the detriment of a superb one? (IE don't fix what's not broken).

I've seen foobar has it as an option, I might have a muck about when I get home...

[bobbasrah]

The sampling theorem suggests that upsampling ..................It is possible to make lousy recordings at all resolutions and sample rates!

Well :eyebrows: Couldn't have put it better myself, or at all in fact.:scratch:
Apart from the last bit that is....:ner:

[serendipitydawg]

http://theartofsound.net/forum/showthread.php?t=9215


Have a butcher's at this thread started by Will. Some of us think upsampling is "something for nothing"