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Post by awachter on Dec 31, 2016 16:57:03 GMT
I have been looking into getting a DAC for my 2011 Mac Mini Server to connect to my analog amplifier. First, I thought that the DAC (via USB, optical, etc.) would take the raw music data directly from my Mac in whichever format it was stored on iTunes (MP3, AAC, Apple Lossless, etc.) and then convert into analog. But looking into the spec sheets of various DACs, I noticed that DACs do not support the "raw audio data i.e. MP3, AAC, etc." formats as digital input but only PCM (at various bit depths and sampling rates), DSD, etc. This means that my Mac (or any other computer for that matter) needs to do the conversion from, say, MP3 to PCM 16 bit/44.1kHz internally. Now my question is: can this conversion be done mathematically i.e. digitally with DSPs or does my Mac need to do a D/A conversion (from, e.g. MP3 to analog) followed by an A/D conversion (back to PCM)? Also, assuming this can be done digitally, does this process add additional noise/distortion?
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Post by Hexspa on Jan 1, 2017 4:54:31 GMT
Hi awachter.
I don't know.
But I'll guess compression and decompression happen in a software codec
whereas the converters are just to go between analog and PCM.
So: Analog->hardware conversion to PCM->Memory->Software conversion to file format->
digital file
->decode to PCM->conversion to analog->sound.
Whether compression is used or not, something has to turn the PCM data into a file format - I don't think this is done at conversion.
Here's a quote from another site:
-G
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Post by arnyk on Jan 2, 2017 12:30:42 GMT
I have been looking into getting a DAC for my 2011 Mac Mini Server to connect to my analog amplifier. First, I thought that the DAC (via USB, optical, etc.) would take the raw music data directly from my Mac in whichever format it was stored on iTunes (MP3, AAC, Apple Lossless, etc.) and then convert into analog. But looking into the spec sheets of various DACs, I noticed that DACs do not support the "raw audio data i.e. MP3, AAC, etc." formats as digital input but only PCM (at various bit depths and sampling rates), DSD, etc. This means that my Mac (or any other computer for that matter) needs to do the conversion from, say, MP3 to PCM 16 bit/44.1kHz internally. Now my question is: can this conversion be done mathematically i.e. digitally with DSPs or does my Mac need to do a D/A conversion (from, e.g. MP3 to analog) followed by an A/D conversion (back to PCM)? Also, assuming this can be done digitally, does this process add additional noise/distortion? ADC's and DACs work with a short list of hardware-oriented data formats. Typically the electrical input to a DAC and the electrical output of an ADC is a serial data stream of uncompressed data. A device may be mono, stereo or multichannel but most are stereo and thus work with two uncompressed stereo channels that are interleaved using time division multiplexing. Very few ADCs and DAC chips have on-chip lossless or lossy data compression features. That is most often done using a CPU or DSP running some kind of software or firmware. Firmware is just software that was burned or lithographed into dedicated storage on the chip. There are chips that have both digital<->analog converters and DSPs and/or general purpose CPUs on them, but the functions are still separated on the chip.
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Post by awachter on Jan 7, 2017 3:02:39 GMT
Thank you for your response!
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Post by Ethan Winer on Jan 7, 2017 19:03:55 GMT
Thanks Arny for your participation here.
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Post by awachter on Jan 8, 2017 16:33:52 GMT
Another question related to DACs: I noticed that some DACs (at least the ones I've been playing with) seem to be using mechanical relays internally - not exactly sure why but I suppose it has to do with audio muting until the DAC has acquired the digital signal from the input source. So there is a very audible "click" at the beginning and at the end of a track. I found this quite annoying. Other than simplicity and cost, are there reasons why they are using mechanical relays as opposed to doing the muting electronically (the DACs I've been playing with were $1,000+ DACs)? I haven't been able to figure out whether or not a particular DAC uses mechanical relays by looking at the manufacturer provided spec sheet. Does anyone know of DACs that are NOT using mechanical relays for audio muting?
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Post by arnyk on Jan 9, 2017 3:03:07 GMT
IME, based on personal experience with dozens of products. most DACs do not have relays. If this is a critical feature for you to obtain or avoid, simply choose from the 400 or so audio DACs on the market to obtain the features you desire.
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Post by Ethan Winer on Jan 10, 2017 19:33:43 GMT
That click is probably the DAC setting or resetting its playback sample rate. I have my sound card set for 44.1 KHz, but if I play a 48 KHz file I hear a click just like you describe. So maybe you can change the default sample rate in the DAC's control panel or some such?
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Post by awachter on Jan 11, 2017 4:33:51 GMT
It may be related to that. But even if I set the default sample rate to match that of my Mac Mini, the click occurs whenever there is a transition from no input to input (or vice versa). So when I stop a track in iTunes and then play a new track, there are two clicks (the first when the old track stops playing and the second when the new track starts playing). My question really is why in this day and age anybody would want to use a mechanical relay and not just handle everything electronically i.e. without the annoying click? I listen mostly to classical music and the clicking between say, the end of a first movement and the beginning of a second movement Adagio in a symphony or piano concerto just drives me crazy.
BTW: I love your book The Audio Expert!
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Post by arnyk on Jan 11, 2017 16:44:38 GMT
It may be related to that. But even if I set the default sample rate to match that of my Mac Mini, the click occurs whenever there is a transition from no input to input (or vice versa). So when I stop a track in iTunes and then play a new track, there are two clicks (the first when the old track stops playing and the second when the new track starts playing). My question really is why in this day and age anybody would want to use a mechanical relay and not just handle everything electronically i.e. without the annoying click? I listen mostly to classical music and the clicking between say, the end of a first movement and the beginning of a second movement Adagio in a symphony or piano concerto just drives me crazy. BTW: I love your book The Audio Expert! You are correct in thinking that muting and input selection can be done purely electronically in a highly effective manner, and for just pennies. However, we're talking golden ear audio here, and in that market there are considerable numbers of potential customers who feel more secure with mechanical relays.
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Post by Ethan Winer on Jan 12, 2017 18:05:08 GMT
If there's a relay inside, you should also hear a mechanical click coming from inside the unit. Do you hear that with your audio volume turned all the way down?
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Post by awachter on Jan 15, 2017 18:28:43 GMT
Yes, I do. The click is definitely from a relay.
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Post by arnyk on Jan 24, 2017 18:02:20 GMT
If there's a relay inside, you should also hear a mechanical click coming from inside the unit. Do you hear that with your audio volume turned all the way down? Ther eis a There is a kind of relay called a reed relay. They are actually ideal for audio line level signals and have been used in some very expensive and highly engineered large format mixers as well as other studio gear. They can be very close to being perfectly silent.
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Post by Ethan Winer on Jan 25, 2017 18:59:19 GMT
^^^ Yes, good point about reed relays being quiet.
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sylva
New Member
Posts: 14
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Post by sylva on Aug 3, 2019 19:17:17 GMT
Hi.
I found this thread and have a question. In one of my computers I have the Delta44. It's a very good card, but M-Audio didn't write Windows 10 drivers for it, so I am facing the important decision of acquiring an interface that I can connect to 2 computers. Since I could connect the interface through a USB switched hub, it need not have two inputs. I thought about the choice between a Mackie Big Knob, Focusrite Scarlett 8i8 gen2, or Behringer umc404HD. However, no matter what interface I research, a good number of reviews by those who bought them have serious issues with the items. Any opinion?
Thanks, John.
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