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  #11  
Old 06-20-2003, 08:59 PM
Doc Doc is offline
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Default Re: 44 or 48

Quote:
Originally posted by StainedClass:
...What if I have music that is going to be for video and destined for CD too?
<font size="2" face="Verdana, Arial">That quite often occurs.
What I usually do is decide on the most important format. In other words, is the sound quality more important on the video or the CD release? Is the material a music video or a movie with a soundtrack?
What you choose will usually depend on the intended market and the genre of the material. Your opinion on SRC will obviously play a part in your decision too.
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  #12  
Old 06-20-2003, 11:50 PM
dkrz dkrz is offline
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Default Re: 44 or 48

Quote:
For a start, look at Multirate Digital Signal Processing by Crochiere and Rabiner (see FAQ section 1.1).
Almost any technique for producing good digital low-pass filters will be adaptable to sample-rate conversion. 44.1:48 and vice-versa is pretty hairy, though, because the lowest whole-number ratio is 147:160. To do all that in one go would require a FIR with thousands of coefficients, of which only 1/147th or 1/160th are used for each sample--the real problem is memory, not CPU for most DSP chips. You could chain several interpolators and decimators, as suggested by factoring the ratio into 3*7*7:2*2*2*2*2*5. This adds complexity, but reduces the number of coefficients required by a considerable amount.
[From Lou Scheffer:]
Theory of operation: 44.1 and 48 are in the ratio 147/160. To convert from 44.1 to 48, for example, we (conceptually):
1. interpolate 159 zeros between every input sample. This raises that data rate to 7.056 MHz. Since it is equivalent to reconstructing with delta functions, it also creates images of frequency f at 44.1-f, 44.1+f, 88.2-f, 88.2+f, ...
2. We remove these with an FIR digital filter, leaving a signal containing only 0-20 KHz information, but still sampled at a rate of 7.056 MHz.
3. We discard 146 of every 147 output samples. It does not hurt to do so since we have no content above 24 KHz. In practice, of course, we never compute the values of the samples we will throw out.
So we need to design an FIR filter that is flat to 20 KHz, and down at least X db at 24 KHz. How big does X need to be? You might think about 100 db, since the max signal size is roughly +-32767, and the input quantization +- 1/2, so we know the input had a signal to broadband noise ratio of 98 db at most. However, the noise in the stopband (20KHz-3.5MHz) is all folded into the passband by the decimation in step 3, so we need another 22 db (that's 160 in db) to account for the noise folding. Thus 120 db rejection yields a broadband noise equal to the original quantizing noise. If you are a fanatic, you can shoot for 130 db to make the original quantizing errors dominate, and a 22.05 KHz cutoff to eliminate even ultrasonic aliasing. You will pay for your fanaticism with a penance of more taps, however.
<font size="2" face="Verdana, Arial">I like pickles, mustard and ketchup on my hamburgers. Oh, cheese too.

[img]images/icons/rolleyes.gif[/img]

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  #13  
Old 06-21-2003, 06:44 PM
wwittman wwittman is offline
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Default Re: 44 or 48

If i know i am going to "mix" inside my system and just burn a CD that way (whcih is rare) i'd stay 44.1 the whole way.
But in most cases i'll go to a real console and mix with each track on its own output to console faders... so in those cases i go 48.

When i compare i hear a big improvement at 48 (and of course an even bigger one at 96k) so i opt for the higher rate.
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  #14  
Old 06-21-2003, 11:50 PM
seancollider seancollider is offline
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Default Re: 44 or 48

I just worked on an album at 96 on HD. Same system for All-American Rejects. Definitely sounded different than 44.1.

Sean
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  #15  
Old 06-22-2003, 12:46 PM
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Park Seward Park Seward is offline
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Default Re: 44 or 48

On all the spec sheets I can find, the frequency response of the 001 and 002 are exactly the same at any sampling rate.

If that is the case, then there is no difference in the sound at any sampling rate on those devices.

I'd like to see any figures anyone may have about the actual top end response of those systems. Are you recording higher frequencies at a higher samplig rate or not?

I did find specs on the Pro Tools HD 192 unit from the Answerbase:
192 I/O @ 192 kHz
Frequency Response: - 0.2 dB @ 50 kHz, - 2.0 dB @ 88 kHz
192 I/O @ 96 kHz
Frequency Response: - 0.2 dB @ 38 kHz, - 2.0 dB @ 44 kHz.
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  #16  
Old 06-22-2003, 02:40 PM
Chaasm71 Chaasm71 is offline
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Default Re: 44 or 48

It'll all come down to the filters they are using on the AD DA converters. If on the 002 @ 96kHz they are still using 20Hz-20kHz, then any high frequency info is getting filtered. Then we are loosing all that hard earned ultrasonic info! Note, the 002 filters aparently still sound better than the 001's, and I'm not debating sound quality, so...no flames on that point, okay! [img]images/icons/wink.gif[/img]

Charlie.
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  #17  
Old 06-22-2003, 06:51 PM
StainedClass StainedClass is offline
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Default Re: 44 or 48

What are the filters?

Is that an electronic componant that prevents aliasing in ad conversion? or DA?
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  #18  
Old 06-22-2003, 07:32 PM
rwhitney rwhitney is offline
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Default Re: 44 or 48

Hey wwittman, thanks for sharing your experience. It accords with mine, though I'm worried it's just my imagination (I've got to do some blind tests soon). I'm curious as to what medium you master to (analog tape, DAT, what?) and then, how do you get it to CD? Also, what converters are you using?

Thanks again.
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  #19  
Old 06-22-2003, 10:21 PM
wwittman wwittman is offline
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Default Re: 44 or 48

I mix to 1/2" analogue 2-track, 15ips NAB no noise reduction.
I get it to CD by mastering at Sterling Sound with george Marino (who's done almost all my records for 20+ years).
George mostly uses the GML (George Massenburg Labs) A-D and i will sometimes use one at the studio as well to take CD's out to listen to during the mix process.
I also make certain that the CD's are encoded off the analogue play head so i am hearing the actual sound off tape... not straight out of the desk... that way i know what my actual final mix sounds like on the tape i'll be bringing to mastering.
When we finally print the final mixes, we then take a GML A-D converted DAT straight off the mix bus as a safety for the 2 track.
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  #20  
Old 06-22-2003, 10:25 PM
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Park Seward Park Seward is offline
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Default Re: 44 or 48

Quote:
Originally posted by StainedClass:
What are the filters?

Is that an electronic componant that prevents aliasing in ad conversion? or DA?
<font size="2" face="Verdana, Arial">Since we can only describe sounds that are less then half the sampling rate (that crazy ole Nyquest), we cannot let any frequencies above that get through to the analog to digital convertor. If we do, we get distortion and an incorrect sample of that sound. It will generate spurious contributions of lower frequencies in the reconstructed signal

The filter is a low pass filter. That is, it only lets frequencies below a certain point through. If it is well designed, it will cause just a little harm to our sound. No filter is perfect.

By using higher sampling rates, we can design a more gentle slope cutoff filter and do less harm to our sound. Also, any ringing and distortions caused by our filter will hopefully be moved up in frequency and out of the audible band.

Digital filters can be created with less distortion than analog filters.
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Analog tape to Pro Tools transfers, 1/4"-2"
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MacPro 6 core 3.33 GHz, OS 10.12.1, 8 GB RAM, PT12.6.1, Focusrite Saffire Pro 40, PreSonus DigiMax, MC Control V3.5, dual displays,
Neumann U-47, Tab V76 mic pre, RCA 44BX and 77DX, MacBook Pro 9,1, 2.3 Mhz, i7, CBS Labs Audimax and Volumax.
Ampex 440B half-track and four-track, 351 tube full-track mono, MM-1100 16-track.
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