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Quality aspects of ADC, Does quality gear makes a difference?
ktf
post Mar 3 2011, 22:45
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Hi all!

Background information (safe to skip rolleyes.gif )
Currently I'm preparing a large archival operation: my musical society has a collection of recordings on compact cassettes from 1980 to 1990, about 140, which I think have to be digitalized to protect them from deteriorating. I have found a nice tape deck (Nakamichi DR-3) but it has to stay at the office of the executive committee. A friend of mine has a nice ADC for this job, a quality portable mixing console with USB out, but it cannot stay at the office as it is more or less public and he doesn't trust everyone there. However, it is too much hassle to bring it every time, as I think this operation will cost about a year: 3 recordings a week. So, I guess I'm stuck with my own ADC: a Creative X-Fi Surround 5.1 USB-card, which is not really made for the job, but I can at least leave it at the office, as it isn't that valuable.

On-topic
That friend of mine that offered me his portable mixing-console with ADC argued that with a cheap ADC all little nuances and details would vanish, so I should look for another solution than using my Creative ADC. That made me think: i'm much more a theoretician than he is, so I was wondering, what makes a high quality ADC? I know the working principle of several ADCs, I can't imagine which link in the chain would be capable of 'erasing details' anyway. How does a non-linearity in an ADC sounds like in practice? And jitter? I guess uncorrelated, random jitter could sound like 'more noise', as it is random. To me it seems a low-quality ADC doesn't add anything but noise and a non-linearity, let alone it could remove things from the signal.

In short: what could a low-quality ADC do with the signal except adding noise? Probably I'm far too short sighted, can anyone enlighten me?


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Music: sounds arranged such that they construct feelings.
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ktf
post Mar 22 2011, 21:56
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Today I made some recordings which made me wonder again on something else, but pretty closely related.

I usually record at the highest setting of the recording device (96kHz, 24bit in this case) because I thought 96kHz brings in some oversampling-like improvements when resampled, and an off-line resampler would do a better job at brick-walling the frequency response, as when directly recording at 44kHz, the filter has to be causal. However, my harddrive is filling up too quickly to my taste (and SD-cards do too), and I don't like deleting original files when I resample them at my computer. It's just the feeling you're throwing away information...

That made me think, would setting the ADC at 96kHz be better anyway? I guess recording 24-bit is nice for some extra headroom (it the other parts have a SNR of over 96dB, which I'm not really sure of) but is there anything like that in the sample rate? Not that long ago, I thought 96kHz would be some kind of nice oversampling, but all ADC do oversample, so would it bring any improvement?

This post has been edited by ktf: Mar 22 2011, 22:00


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Arnold B. Kruege...
post Mar 24 2011, 12:51
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QUOTE (ktf @ Mar 22 2011, 16:56) *
I usually record at the highest setting of the recording device (96kHz, 24bit in this case) because I thought 96kHz brings in some oversampling-like improvements when resampled, and an off-line resampler would do a better job at brick-walling the frequency response, as when directly recording at 44kHz, the filter has to be causal.


I suppose that it might be possible for a software downsampler to in theory do a better job, but back in the real world even average 44/16 converters pass ABX tests related to sonic transparency.

QUOTE
However, my harddrive is filling up too quickly to my taste (and SD-cards do too), and I don't like deleting original files when I resample them at my computer. It's just the feeling you're throwing away information...


I think you need to distinguish between information and data. There is no doubt that transcribing audio at higher sample rates increases the amount of data. However gathering as much data as is possible is not the essence of recording. Gathering useful information is the essence of recording. If the data makes no sense and adds nothing, then it is clearly not relevant information.

For example I have an audio interface that records at 24/192 and has 107 dB dynamic range, and I've verified this in lab tests. However, if use it to record at 24/192 the resulting recording has only about 80 dB SNR if I measure noise over the full 96 KHz bandpass of the device. To obtain the 107 dB number I have to follow good practice, which is to measure noise over a reasonable bandwidth which is 20-20 KHz. If I look at the spectral content of the actual recordings I make at the 192 KHz sample rate, most of what I record above 20 KHz is noise, both random and also spurious coherent signals such as harmonics from switchmode power supplies elsewhere in the room.

In short, if I used this audio interface at 24/192 to transcribe LPs or cassette tapes, I'm spinning my wheels by wasting time and disk space with noise that contributes nothing to my enjoyment of the music. Even if I use it to record live music, I'm still spinning my wheels because I know for sure that I can brick wall my recordings @ 20 KHz with no audible change whatsoever.

QUOTE
That made me think, would setting the ADC at 96kHz be better anyway? I guess recording 24-bit is nice for some extra headroom (it the other parts have a SNR of over 96dB, which I'm not really sure of) but is there anything like that in the sample rate? Not that long ago, I thought 96kHz would be some kind of nice oversampling, but all ADC do oversample, so would it bring any improvement?


You have to ask yourself - are you working for your enjoyment or are you a slave to the excess performance of your equipment? The current the SOTA of electronics is that we can use reasonably priced electronics to overkill just about anything in audio except for the actual limitations to the sound quality of our recordings which have nothing to do with 24 bits or very high sample rates. We still can't overcome the basic limitations of recording music in rooms with microphones and we still can't overcome the limitations of listening via speaker or headphones.
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Posts in this topic
- ktf   Quality aspects of ADC   Mar 3 2011, 22:45
- - DVDdoug   The only thing I'd even consider is noise. A...   Mar 3 2011, 23:52
|- - ktf   QUOTE (DVDdoug @ Mar 3 2011, 23:52) The o...   Mar 4 2011, 16:19
- - DonP   One thing that's been an issue in the past is ...   Mar 4 2011, 17:08
- - DVDdoug   QUOTE So, the THD+N (for distortion and non-linear...   Mar 4 2011, 20:51
|- - ktf   QUOTE (DVDdoug @ Mar 4 2011, 20:51) With ...   Mar 4 2011, 23:42
|- - Notat   QUOTE (ktf @ Mar 4 2011, 16:42) It also r...   Apr 5 2011, 15:18
|- - ktf   QUOTE (Notat @ Apr 5 2011, 15:18) Apologi...   Apr 5 2011, 15:23
|- - Notat   In your setup, there are two ground paths between ...   Apr 5 2011, 18:49
|- - Arnold B. Krueger   QUOTE (Notat @ Apr 5 2011, 13:49) In your...   Apr 6 2011, 14:37
- - Arnold B. Krueger   QUOTE (ktf @ Mar 3 2011, 16:45) That frie...   Mar 8 2011, 13:38
|- - ktf   QUOTE (Arnold B. Krueger @ Mar 8 2011, 13...   Mar 8 2011, 18:02
|- - Arnold B. Krueger   QUOTE (ktf @ Mar 8 2011, 12:02) QUOTE (Ar...   Mar 8 2011, 19:09
|- - ktf   QUOTE (Arnold B. Krueger @ Mar 8 2011, 19...   Mar 8 2011, 21:25
||- - Arnold B. Krueger   QUOTE (ktf @ Mar 8 2011, 15:25) QUOTE (Ar...   Mar 8 2011, 22:59
||- - mixminus1   QUOTE (Arnold B. Krueger @ Mar 8 2011, 13...   Mar 8 2011, 23:17
|- - Kees de Visser   QUOTE (Arnold B. Krueger @ Mar 8 2011, 20...   Mar 15 2011, 13:34
|- - Arnold B. Krueger   QUOTE (Kees de Visser @ Mar 15 2011, 08:3...   Mar 24 2011, 12:32
|- - DonP   QUOTE (Arnold B. Krueger @ Mar 24 2011, 06...   Mar 24 2011, 12:53
- - ktf   QUOTE (Arnold B. Krueger @ Mar 8 2011, 22...   Mar 13 2011, 22:49
- - ktf   Today I made some recordings which made me wonder ...   Mar 22 2011, 21:56
|- - Arnold B. Krueger   QUOTE (ktf @ Mar 22 2011, 16:56) I usuall...   Mar 24 2011, 12:51
|- - ktf   Woops, I forgot about this topic. I have set track...   Apr 5 2011, 10:19
- - 2Bdecided   Cleaning and demagnetising the heads, matching the...   Apr 6 2011, 15:14
- - Arnold B. Krueger   QUOTE (ktf @ Mar 3 2011, 17:45) Hi all...   Jun 6 2012, 13:20


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