Tag: mixpre

Approved Media – MixPre II Series and MixPre Series

Sound Devices extensively tests removable recording media with the MixPre-3 II, MixPre-6 II, MixPre-10 II, and the legacy MixPre-3, MixPre-6, and MixPre-10T audio recorders.

SD Cards

Sound Devices recommends its own brand of SD card – the SAM-64SD and SAM-128SD, listed below – which has been optimized and extensively tested to ensure fast and flawless performance when used with the MixPre Series of recorders. However, many SD, SDHC, and SDXC cards from other reputable manufacturers, like Delkin or SanDisk, that meet or exceed class 10 speeds are acceptable.

For best media performance, Sound Devices recommends occasionally performing a full reformat of an SD card per the “Overwrite Format” method from the SD Association. The Overwrite Format deletes file/directory entries by initializing file system parameters of the card (same as with Quick Format), and erases all data by overwriting the user data area completely. The Overwrite Format takes more time to complete than the Quick Format method. More information can be found on the SD Association’s website. Please note that all files stored on the card will be lost during the formatting process. After using the SD Memory Card Formatter, the card will still need to be formatted in the mixer-recorder.

MicroSD to SD Card adapters are not recommended for use in any MixPre Series audio recorder.

Tested cards:

Type Size Brand Model
SD Card 64 GB Sound Devices SD/SDXC, UHS-II, 240 MB/s (read) and 100 MB/s (write)
SD Card 128 GB Sound Devices SD/SDXC, UHS-II, 240 MB/s (read) and 100 MB/s (write)
SD Card 32 GB Amplim Amplim SDXC UHSII V90 32GB
SD Card 64 GB SanDisk Extreme; SDXC/UHS-1,V30, U3, 150MB/s (Model # SDSDXV6-064G-GNCIN)
SD Card 64 GB Integral Ultima Pro Integral Ultima Pro SDXC I V30 64GB
SD Card 64 GB Amplim Amplim SDXC UHSII V90 64GB
SD Card 128 GB Freetail Freetail Evoke Pro 128GB V60, UHS II
SD Card 128 GB Wise Wise SDXC II 285MB/s 128GB

USB Thumbdrives

All MixPre II models and the MixPre-10T supports automatic copying of active projects from its SD card to a USB thumbdrive inserted into its USB-A port. For reliable operation, Sound Devices highly recommends only using approved USB thumbdrives, listed below:

NOTE: Because USB thumbdrives vary massively in performance, others not listed here may work, but their reliability cannot be guaranteed.

Type Size Brand Model
USB Thumbdrive 64 GB Samsung USB 3.0 Flash Drive Fit (MUF-64BB/AM)
SanDisk Cruzer Fit USB 2.0 Low-profile Flash Drive (SDCZ33-064G-B35)
32 GB Samsung USB 3.0 Flash Drive Fit (MUF-32BB/AM)
SanDisk Cruzer Fit USB 2.0 Low-profile Flash Drive (SDCZ33-032G-B35)

Unapproved Media

The media listed below currently fail our intensive media approval tests. We highly recommend NOT using this media.

Type Size Brand Model
SD Card 64 GB SanDisk Extreme PRO 170MB/s, 64 GB
SD Card 128 GB SanDisk Extreme PRO 170MB/s, 128 GB

Announcing the MixPre II Series

REEDSBURG, WI, AUGUST 29, 2019 – Sound Devices is pleased to announce the MixPre-3 II, MixPre-6 II, and MixPre-10 II, successors of the award-winning MixPre Series. All models of the MixPre II Series function as recorders, mixers, and USB interfaces, and are suited for a wide range of applications, with features for podcasters, musicians, indie filmmakers, journalists, field recordists, and production sound mixers alike. The first generation MixPre-10T won the prestigious Cinema Audio Society (CAS) Award for Outstanding Product in Production.

Continue reading “Announcing the MixPre II Series”

Sample 32-bit float and 24-bit fixed WAV files

These samples were recorded on a MixPre-3 II to demonstrate the advantage of using 32-bit float WAV files for recording. We split a signal from a MKH40 mic into two MixPre-3 IIs, one recording 24-bit fixed WAVs, and the other 32-bit float WAVs. We then applied too much gain to loud dialogue. Low-cut was set to 80 Hz, and no limiters were active. Both the original 32-bit float and 24-bit fixed file are heavily distorted and unusable.

These files were imported into iZotope RX7, and -30 dB of gain was applied to each file. As you can see and hear, the 32-bit float files scale back perfectly, and the 24-bit files do not.

Included in the download:

32_bit_float.wav: Original file recorded on MixPre-3 II with too much gain.

32_bit_float_30_dB_atten.wav: 32_bit_float.wav file with -30 dB of gain applied by iZotope, and then re-saved. Notice that this file sounds great and is usable.

24_bit_fixed.wav: Original file recorded on MixPre-3 II with too much gain.

24_bit_fixed_30_dB_atten.wav: 24_bit_fixed.wav file with -30 dB of gain applied by iZotope, and then re-saved. Notice that this file is still distorted and unusable.

32-Bit Float Files Explained

The MixPre II models introduce the ability to record 32-bit floating point WAV files.  For ultra-high-dynamic-range recording, 32-bit float is an ideal recording format. The primary benefit of these files is their ability to record signals exceeding 0 dBFS. There is in fact so much headroom that from a fidelity standpoint, it doesn’t matter where gains are set while recording. Audio levels in the 32-bit float WAV file can be adjusted up or down after recording with most major DAW software with no added noise or distortion. To understand the nuts and bolts of 32-bit files, keep reading. This paper discusses the differences between 16-bit fixed point, 24-bit fixed point, and 32-bit floating point files.

16-bit Files

Traditional 16-bit WAV files store uncompressed audio samples, where each sample is represented by a binary number with 16 digits (binary digit = “bit”). These numbers are “fixed-point”, because they are whole numbers (no decimal point). A 16 bit number in binary form represents integers from 0 to 65535 (216). 

Numeric values represent a discrete voltage level corresponding to the signal amplitude. 65535 represents the maximum amplitude (loudest) the signal can be, and the lowest values represent the noise floor of the file, the lowest bit toggling between 0 and 1. Since there are 65536 levels, the noise = (1/65536). 

Putting this noise in dB form:

dBnoise = 20 x log (1/65536) = -96.3 dB 

The max level in dB form:

dBmax = 20 x log (65536/65536) = 0 dB

The maximum dynamic range that can be represented by a 16 bit WAV file is (0 dB – (-96.3 dB)) = 96.3 dB

16-bit WAV files, whether in a digital audio recorder or DAW software, call the largest signal captured 0 dBFS, meaning 0 dB relative to the full-scale (of the file). So, 16-bit WAV files can store audio from 0 dBFS down to -96 dBFS. Each audio sample consumes 16 bits of space on a hard disk or memory, and at a 48 kHz sampling rate this means that 16 x 48,000 = 768,000 bits per second are needed to store a single channel 16-bit, 48 kHz file. 

24-bit Files

24-bit (fixed point) WAV files improve on the amplitude resolution of 16-bit by extending the 16 bit word, adding 50% more bits, to make a 24 bit word. 

With more numbers there are more discrete voltage levels to divide the audio signal. 24-bit in binary notation ranges from 0 to 16,777,215 (224)

Doing the same math with 24-bit files to calculate the noise level and the maximum levels results in the following:

dBnoise = 20 x log (1/16777216) = -144.5 dB

dBmax = 20 x log (16777216/16777216) = 0 dB

The dynamic range of a 24-bit (fixed point) file is (0 dB – (-144.5 dB)) = 144.5 dB

Just like for 16-bit files, audio recorders and DAW software call the largest signal in a 24-bit WAV file 0 dBFS. Each audio sample consumes 24 bits of space of digital storage, and at a 48 kHz sample rate, this means that 24 x 48,000 = 1,152,000 bits per second are needed for a single channel, 24-bit, 48 kHz file. For an increase of 50% in storage space compared to 16-bit files the dynamic range captured goes from 96 dB up to 144 dB, a substantial increase in performance. Presently 24-bit, 48 kHz WAV files are the most widely-used files in the professional audio community.

32-bit float

Compared to fixed-point files (16- or 24-bit), 32-bit float files store numbers in a floating-point format. This is fundamentally different than fixed point, because numbers in these WAV files are stored with “scientific notation”, using decimal points and exponents (for example “1.4563 x 106“ instead of “1456300”). This difference is significant because much larger and smaller numbers can be represented compared to a fixed-point representation. The formatting and encoding of the 32-bit word is not intuitive–it has been optimized for computers to be able to perform common math functions on it rather than for human-readability. The first bit indicates a positive or negative value, the next 8 bits indicate the exponent, and the last 23 bits indicate the mantissa. More info is available regarding this format (called IEEE-754).

The largest number which can be represented is ~3.4 x 1038, and the smallest number is ~1.2 x 10-38. Doing the math:

dBnoise = 20 x log (1.2 x 10-38) = -758 dB

dBmax = 20 x log (3.4 x 1038) = 770 dB

The dynamic range that can be represented by a 32-bit (floating point) file is 1528 dB. Since the greatest difference in sound pressure on Earth can be about 210 dB, from anechoic chamber to massive shockwave, 1528 dB is far beyond what will ever be required to represent acoustical sound amplitude in a computer file. 

There is one other aspect of 32-bit float files which is not immediately obvious. Files recorded with 32-bit float record sound where 0 dBFS of the 32-bit file lines up with 0 dBFS of the 24- or 16-bit file. Keep in mind that unlike the 24- or 16-bit files, the 32-bit file goes up to +770 dBFS. So compared to a 24-bit WAV file, the 32-bit float WAV file has 770 dB more headroom.

Modern, professional DAW software can read 32-bit float files. When a DAW first reads a 32-bit file, signals greater than 0 dBFS may first appear clipped since, by default, files are read in with 0 dB of gain applied. By applying attenuation to the file in the DAW, signals above 0 dBFS can be brought below 0 dBFS, undistorted, and used just like any 24- or 16-bit file.

For 32-bit float recording, exact setting of the trim and fader gain while recording is no longer a worry, from a fidelity standpoint. The recorded levels may appear to be either very low or very high while recording, but they can easily be scaled after recording by the DAW software with no additional noise or distortion. This can be seen with these sample files. This is the same source, one recorded with 24-bit fixed and the other with 32-bit float. Both files appear clipped when initially read into DAW software, but the 32-bit file’s gain can be scaled by the DAW.

Each audio sample for 32-bit float files consumes 32 bits of space on a hard disk or memory, and for a 48 kHz sampling rate, this means that 32 x 48,000 = 1,536,000 bits per second are needed for 32-bit, 48 kHz files. So for 33% more storage space compared to 24-bit files, the dynamic range captured goes from 144 dB up to, essentially, infinite (over 1500 dB). But more importantly, audio signals above 0 dBFS are preserved in the file, rendering clipped audio a thing of the past.

Recording 32-bit float audio files, along with high performance analog and digital electronics that can take advantage of its massive dynamic range, offer sound designers and sound mixers a  new way to record audio. This is especially useful for applications where very loud, unexpected sounds can be captured without the use of limiters. The trade-off for using 32-bit float files is larger file sizes compared to 24-bit files.

For more information, please see our related Support Articles:
https://www.sounddevices.com/the-32-bit-workflow/
https://www.sounddevices.com/32-bit-float-usb-audio-with-the-mixpre-ii-series/

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