usb, spdif, or usb to spdif converter

Generally, a usb-to-spdif converter is good for two scenarios:

1. you have a really bad usb source (like a computer or, especially, a laptop) where there is a not of noise, power supply is not good or the source usb transmit clock is not good.  If you have a computer, you can get an excellent usb card with TCXO or OCXO click such as the Jcat or Pink Faun.

2. Your DAC has a very poor usb receiver board.  This can mean the usb receiver chip architecure is poor or if the usb-to-i2s module doesn't have a good clock or power supply line.

If you have a good transport/source and a good DAC with a really good USB, then you generally don't need a usb-to-spdif converter.  That being said, I generally like the sound of SPDIF, especially when I can use high end AES/EBU cables on source and dac.  The engineers from Pink Faun (who make USB, SPDIF and I2S computer cards) have the opinion that usb audio does not sound as good as spdif audio.  However, you need a really good SPDIF source and cable to reveal this.

In some situations, a usb-to-spdif converter with an extremely high end clock and power supply can be better than what you have.  These are products such as the Innous Pheonix reclocker or the Audio-GD DI-20 audio interfaces.  The Singxer SU-6 is okay, but there are some DACS that actually have a better usb-to-i2s module.

It depends. One way to look at it is:  If your DAC is better than your source then USB. Otherwise SP/DIF. The USB is retimed by the DAC, the SP/DIF, AES is not. But basically you have to try both. 
 

Never convert anything.

The USB interface is a data packet interface. Granted, you can improve music quality if you put in a better usb transmitter/source device. However, the receiving dac is going to have to un-wrap that usb data packet to get the actualy music file data (such as 16/44.1 or 24/96, etc.). Then it has to generate the individual channel pulses at the exact clock timing (such as 44.1khz). It outputs this on two i2s data lines that feed directly into the DAC chip. That is why I talk about the quality of the USB-to-I2S module in the DAC. If you have a really good one, then the USB input can be used.

When you use S/PDIF, the DAC has to unwrap this into two separate i2s data streams (for the dac chip). However, the pulses are pretty much already there and are being sent with the actual clock timing required (i.e. 44.1kz or 96khz, etc.), so no re-clocking /re-generating has to be done by the DAC when compared to USB input.

These high end usb-to-spdif converters are a very high end version of the "USB-to-I2S" module in the dac. This can be a significant improvement over using the DAC USB input.

Never convert anything.

Converting USB to i2s works for me.

Many thanks and hope you all had a wonderful Thanksgiving.  I am running a windows 7 desktop computer (a 12 year old gateway) usb output to an idsd micro dac for both music and blu ray movies.  I would rather use a stand alone player.  However, when I compared the computer sound (usb to the usb input of the dac) to the player's sound (coax to the same dac - using a newer sony blu ray player) the computer's sound was MUCH better in every way.  Any thoughts on getting equivalent sound via coax from a player would be appreciated.   

I've got a music fidelity sitting here doing nothing if you want a fabulous deal on a USB SPDIF converter.  This is the 24/96 version.

Which is better probably depends upon your hardware.  The SPDIF is more generic, I think, so it might all depend on how your DAC handles USB.  DACs convert USB to I2S internally, so that if your DAC does this well, no need for external USB to I2S device like the Singxer.  

Ultimately, a sound test is best.  However, for example, if the USB board in the DAC gets its 5V internally, as opposed to through the USB cable, it is likely the best way to go.  This is something to consider when buying a new DAC.

The sony blu ray players are an okay transport for digital coax s/pdif, but they are certainly not the best.  To be honest, most of the bluray players out there are not the best S/PDIF transport.  If you want a really good player/transport for both movies and music, look for a used Oppo 103 or 203 player and then upgrade it with a linear power supply from oppomod.com.

Also, your coax digital cable will affect the sound quality you get as well.  Make sure you have a good one.

Otherwise, you can run with a computer if you want.

One more thing.  If you are running the ifidac using coax spdif, you may want to look at an outboard USB linear power supply, like the LKS:

https://www.ebay.com/itm/133687208763?hash=item1f2060eb3b:g:EVwAAOSw-4BXX8qS

Unless you charge the Ifi DAC separately and then unplug the usb cable before turning it on with coax input.

Thank you. After reading the last 2 posts my gut tells me that my computer is a better transport than the sony BR player. Also I am playing rips from the computer's hard drive so that may partially explain the difference.  I power the idsd dac from its battery, not the usb cable, and it does sound better that way.  However, I have heard many times, on this forum and others, that the usb interface should never be inside the dac - hence the reason for my question regarding the usb to spdif converter. My dac is around 7 years old and I'm due for an upgrade - any recommendations new or used up to 1,000 that would best the idsd? One that was recomended was a used monarchy audio M24 but they are hard to come by.       

"the usb interface should never be inside the dac" ??? 

That's news to me.  They are on most of the acknowledged great DACs. 

Ah, I was thinking of mentioning another alternative, but I did not because of the complexity.  However, since you stated that you are actually ripping your BD/DVD discs onto computer files and then playing them, there is another option.  (ripping is usually too complex a process for most people).

You can look at one of the high end media players, such as Zapitti, Zidoo or Dune.  You would just take your ripped movies and copy them to a SSD which can be inserted into these media players.  These will likely have better video quality than your computer.

The Zappiti Reference actually has a built-in DAC uses ESS saber dac chips and full linear power supplies for everything:

https://www.zappiti.us.com/product-page/zappiti-reference

It's way over your stated budget, but it's an all-in-one box.  The DAC may actually have more resolution and detail than your ifi (it's difficult to tell).

Another option with high-end power supplies and dac is Dune Ultra 4K:

https://www.dune-hd.com/collections/frontpage/products/dune-hd-ultra-vision-4k

Dune has a lesser model with smaller linear power supply and uses AKM dac instead of ESS, but it's only $699:

https://www.dune-hd.com/collections/frontpage/products/dune-hd-max-vision-4k

If you want to try one of these media players as a digital coax transport only, the cheapest way to go is a Zidoo Z10pro:

https://shop.zidoo.tv/products/zidoo-z10pro-new-arival-rtd1619dr-media-player-4k-uhd-android-9-0-dolby-vision-support-hard-drive-up-to-14tb-2g-32g

Then add a good external linear power supply for this such as Farad Super3 (or Keces if you have a budget, or even a cheap china ebay Teradak).

If you just want to get a really good upgrade DAC (which will likely sound better than the Zappiti/Dune anyways), here's a short list at the $1k price point:

R2R resistor ladder dacs (generally more laid back sound, but more tonally thick/rich):

Audio-GD R-1

Denafrips Ares II (currently on sale at shenzhenaudio.com)

ESS saber dacs (more forward, detailed, exciting, revealing):

Audio-GD D-77 (with full clock upgrades)

Gustard DAC-X22

Other:

--USED-- PS AUDIO Stellar Gain Cell DAC currently on audiogon for $995.

many thanks - actually I do find ripping too complex and cumbersome - the only reason I am doing it is because the computer sounds so much better than the sony br player -  curious - what is the other (complex) alternative?

the other complex alternative is looking at those high end media players (Zappiti, Zidoo, Dune).  That requires you to rip the movies into a file for playback.

If you just want to through a BD/DVD disc into a player and want a better result, get a used Oppo 103 or 203, then upgrade the linear power supply (oppomod.com).